Phenolic carbon tailored for the removal of polar organic contaminants from water: A solution to the metaldehyde problem?

Accepted Manuscript Phenolic carbon tailored for the removal of polar organic contaminants from water: a solution to the metaldehyde problem? R. Busquets , O.P. Kozynchenko , R.L.D. Whitby , Steve Tennison , Andrew B. Cundy PII:

S0043-1354(14)00341-8

DOI:

10.1016/j.watres.2014.04.048

Reference:

WR 10650

To appear in:

Water Research

Received Date: 16 November 2013 Revised Date:

8 April 2014

Accepted Date: 29 April 2014

Please cite this article as: Busquets, R., Kozynchenko, O.P., Whitby, R.L.D, Tennison, S., Cundy, A.B., Phenolic carbon tailored for the removal of polar organic contaminants from water: a solution to the metaldehyde problem?, Water Research (2014), doi: 10.1016/j.watres.2014.04.048. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Water spiked with metaldehyde O O O

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Phenolic carbon tailored for the removal of polar organic contaminants

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from water: a solution to the metaldehyde problem?

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R. Busquets1-4, O.P. Kozynchenko2, R. L. D Whitby3, Steve Tennison2, Andrew B.

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Cundy1*

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School of Environment and Technology and 3School of Pharmacy and Biomolecular

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Sciences, University of Brighton, Brighton, BN2 4GJ. United Kingdom.

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MAST Carbon International Ltd. Jays Close Basingstoke, Hampshire RG22 4BA, UK Kingston Universty, Faculty of Science, Engineering and Computing, Kingston Upon

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Thames, Surrey, KT1 2EE.

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Corresponding author phone: +44 (0)1273642270; e-mail: [email protected]. University of Brighton

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ABSTRACT

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Current water treatment technologies are inefficient at treating water contaminated with

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metaldehyde, an 8-member cyclic tetramer of acetaldehyde widely used as a molluscicide

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in large-scale agriculture and in gardens, and which has been frequently observed to

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breach European regulatory limits in the UK due to its high solubility and frequent use.

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Here, we examine the controls on metaldehyde adsorption onto activated phenolic

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carbon, namely the influence of activation degree, pore size distribution, particle size,

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point of zero charge and surface functionalisation, by synthesising “tailored” carbons

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from phenolic resin. Metaldehyde adsorption has been found to be independent of

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specific surface area (SBET), which is highly unusual for an adsorption process, and is

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favoured in carbons with (a) high microporosity with narrow pore size distribution, (b)

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presence of mesopores which allow efficient diffusive transport, and (c) an absence of

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negatively charged functional groups. The maximum adsorption capacity of the phenolic

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resin-derived carbons, tested at an elevated (i.e. exceeding environmental levels) water

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concentration of 64 mg metaldehyde/L, was 76 mg metaldehyde/g carbon compared with

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13 mg metaldehyde/g carbon in industrial granular activated carbon (GAC). The phenolic

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resin-derived carbons and GAC showed similar adsorption kinetics with maximum

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metaldehyde uptake occurring within 30 minutes under batch adsorption conditions,

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although adsorption isotherms indicate much stronger adsorption of metaldehyde on the

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phenolic resin-derived carbons. Adsorption efficiency for metaldehyde was maintained

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even in the presence of high background concentrations of organic matter and inorganic

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salts, indicating the potential utility of these “designer” carbons in waste and/or drinking

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water treatment.

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Keywords: metaldehyde; phenolic carbon; water treatment; wastewater 1. INTRODUCTION The environmental objectives of the EU Water Framework Directive (WFD) (2000) seek

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to prevent the deterioration of ground and surface water bodies, and achieve good

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ecological and chemical status in water courses within the EU Member States by 2015

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(Council of the European Communities, 2000). This requires the management of a range

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of chemicals in the environment, including pesticides, and their supply to water courses.

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In addition, within the Drinking Water Directive, relatively stringent concentration limits

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for pesticides have been adopted for drinking water (Council of the European

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Communities, 1998). However, given the diversity of situations in the various regions of

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the Community Member states and the technological limitations of many current water

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purification processes, certain contaminants are allowed to deviate from relevant

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directives in specific areas if they have been granted with a derogation; which is valid for

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a limited period of time when required standards cannot be met for particular

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contaminants and such contamination does not constitute a danger to human health

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(Council of the European Communities, 1998). Metaldehyde, 2,4,6,8-tetramethyl-1,3,5,7-

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tetraoxacyclooctane, is one such contaminant, which is inefficiently treated in current

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wastewater treatment plants (WWTPs) (House of Commons, 2011; Water UK, 2013). It

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is commonly used as a molluscicide in agriculture and domestic gardening to control

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snails and slugs, and its large-scale application provides a potential contamination issue

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in areas where long wet seasons require the control of these plant pests (Bonton et al.,

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2012; Fabro et al., 2012). For example, in the period 2008-2011, 1298

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tonnes of

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metaldehyde were used across the UK, and 4770 tonnes have been used since 1990

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(FERA, 2013).

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Metaldehyde is soluble in water, with a solubility limit of 0.2 g per litre and log P of 0.12

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(both parameters measured at 20 ºC and at pH 5, 6.5, 7.2 and 9, European Food Safety

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Authority, 2010), and has high mobility in the aqueous environment and low affinity for

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suspended particulate matter. In terms of its stability, 50-78% of metaldehyde was

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observed to be degraded to CO2 within 60 days of its application to aerobic soil, but it

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exhibited higher persistence, with mineralization of just 10% after 45 days, in an

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anaerobic soil (European Food Safety Authority, 2010) Metaldehyde’s stability, high

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mobility in soil, and solubility in water under typical environmental conditions implies

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that run-off from treated land provides an uncontrolled input of contamination (European

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Food Safety Authority, 2010). Furthermore, since rain dissolves the pellets through which

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metaldehyde is applied, the molluscicide therefore has to be reapplied after rainy periods,

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which compounds the environmental problem. The current maximum application rate of

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the molluscicide is 700 g metaldehyde/ha/calendar year in the UK (The Metaldehyde

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stewardship group, 2013). Since 2007, metaldehyde has been detected in surface waters

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and in some drinking waters across the UK occasionally well above the standard levels

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set by the Drinking Water Directive (0.1 µg/L) (Council of the European Communities,

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1998, 2000; Water UK, 2011, 2013; Bristol Water, 2012). For instance, during the period

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2008-2011, the water industry measured concentrations of metaldehyde up to 1.08 µg/L

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in some Yorkshire rivers (UK), with peak values more generally ranging between 0.4 and

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0.6 µg/L and occurring during October-December (Kay et al, 2013). While much

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published data refers to the UK, the problem is much wider than in the UK only: in a

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study where pesticides were monitored periodically in ponds in North eastern France (5

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sites located in the Moselle river basin) over the period 2007-2009, metaldehyde was

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detected in more than 50% of the samples at concentrations ranging between 0.03 and

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6.98 µg/L (Lazartigues et al, 2012). Metaldehyde is used widely in other regions beyond

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NW Europe (e.g. Gavin et al, 2012; Zhongguo et al. 2013). Therefore, water can

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potentially be contaminated in these areas, although concentrations of metaldehyde in

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surface water in these regions have not been reported to date (to the knowledge of the

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authors).

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The maximum reported concentration of metaldehyde in UK (treated) drinking water is

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just above 1.03 µg/L; detected in November 2007 and in December 2008 (Water UK

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2013). These contamination levels do not imply an immediate health risk since the likely

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intake of metaldehyde is well below the acceptable daily intake (0.02 mg metaldehyde/

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kg body weight) (Water UK, 2011), but they clearly breach regulatory limits.

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The environmental problem posed by metaldehyde is also a challenge for the scientific

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community, who together with water utilities and with the support of the European

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Commission, are studying strategies for its removal and the removal of similar highly

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polar contaminants (Water UK, 2013). Removal by adsorption during tertiary treatment

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of water, typically using activated carbons, is one of the few viable methods to purify

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water contaminated with polar contaminants which show limited reactivity with oxidising

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agents (Teixidó et al., 2011), or where their degradation is affected by background

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organic matter (Autin et al., 2012). When the organic “skeleton” of the contaminant

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however is small, as is the case for molecules such as acrylamide, geosimine, 1,1,1-

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trichloroethane, methyl tert-butyl ether (MTBE) and metaldehyde, the interaction with

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conventional (activated) carbon will not be strong, hence tertiary treatments involving

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granular activated carbon (GAC) are relatively ineffective. Recent work however has

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suggested that “designer” activated carbons (where surface charge and porosity are

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controlled or “tailored” to target specific groups of contaminants) may have significant

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potential in the targeted removal of problem and emerging water contaminants (Ragan et

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al., 2012). Here, we examine the mechanisms governing the uptake of metaldehyde on

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activated carbon, and synthesise optimal (“tailored”) carbon structures to improve

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metaldehyde adsorption and maximise its removal from surface, waste and drinking

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waters.

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2. MATERIALS AND METHODS

Materials. Metaldehyde (CAS 9002-91-9, analytical grade) and 2-chloro-4-ethyl-d5-

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amino-6-isopropylamino-1,3,5-triazine (D5-atrazine) (CAS 163165-75-1, 99% purity)

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were from Sigma Aldrich (UK). Granular Activated Carbon (GAC) was sourced from

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Anglian Water, a major UK water utility. Microporous powdered activated carbons

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(PAC), which had 8-15 µm particle size, were obtained from three major carbon

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producers: Picactiff EPII 8/15, coded as PA, and PICAPURE HP 120 8/15, coded as PP ,

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were obtained from PICA (France); CECA CPW, coded as C was obtained from CECA

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(France); and Norit CGP Super, coded as NS, was obtained from Norit (the Netherlands).

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Carbon synthesis. Activated carbon beads with controlled pore distributions, surface

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functionalisation and activation/ burn-off degree were synthesised from porous phenolic

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resin to examine metaldehyde-carbon interactions. Phenolic carbons in this study are

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designated as nanoporous, nano-mesoporous and nano-macroporous. Custom-made

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porous phenolic resin beads were prepared following a well-established methodology

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where industrial Novolac pre-polymer (Hexion Specialty Chemicals Inc., UK) was cross-

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linked with hexamethylenetetramine (hexamine) in ethylene glycol (EG) solution

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dispersed in an inert mineral oil at 160 ºC (Kozynchenko et al., 2002; Tennison et al.,

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2008; Gardziella et al., 2004). Examples of resin solution compositions used for the

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preparation of corresponding resin precursors are presented in Table 1. Ethylene glycol

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has a dual role in resin preparation: it acts as a solvent and also as a pore former. As

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shown in Table 1, the higher the content of the ethylene glycol in the resin solution

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before cross-linking, the higher the meso/macropore size and volume in the cured resin

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and activated carbon derivatives. After thermal curing, the beads are separated from the

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oil and washed with hot water (80 ºC); carbonised at 800 ºC in a CO2 atmosphere and

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activated to prescribed burn off degrees at 900 ºC.

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When necessary, the surface chemistry has been modified by oxidation with ammonium

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persulphate in H2SO4 (4N), under conditions described elsewere (Salame and Bandosz,

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1999; Wang et al., 2007; Tamai et al., 2006; Seredych et al., 2008). Sulphonic acid

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groups were introduced by derivatising activated phenolic carbons with sulphanilic acid

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(Wang, et al., 2007).

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The introduction of amino groups was carried out by derivatising the carboxylic groups

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of oxidised carbons with thionyl chloride followed by reactions with ethyldiamine or

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N,N-dimethylethyldiamine (Tamai et al., 2006). Phenolic carbons freshly activated in

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carbon dioxide had a point of zero charge (PZC) of approximately 10. Carbons with PZC

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of 8.7 were obtained by impregnation of carbon beads with urea solution followed by

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calcination. Preparation details can be found elsewhere (Seredych et al., 2008). The

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introduction of acidic groups, described above, changed the PZC value to 2.3.

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In this work, the beads denoted as TE3 and TE7 contained cross-linked resin:

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ethyleneglycol at a proportion of 10:15 and 10:25 respectively and were nano-

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mesoporous carbons. The amount of carbon burn-off during the activation in CO2 was

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34% and 55%, respectively, and the particle size studied ranged from 125 to 250µm. The

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beads denoted as TE8 were prepared with a proportion 10: 27 cross-linked resin: ethylene

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glycol respectively, with particle size of 250-500 µm and 65% burn off.

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Characterisation of phenolic resin-derived beads and GAC. Pore size distribution,

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specific surface area (SBET) and pore volume were determined via nitrogen adsorption-

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desorption isotherms, which were carried out on 40mg samples at 77.4K after outgassing

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at 130 ºC for 24h using an Autosorb adsorption analyser (Quantachrome Instruments,

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USA). A density functional theory (DFT) model was used to determine microporosity,

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BJH (Barrett-Joyner-Halenda) and BET (Brunauer-Emmett-Teller) models were used for

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pore characterisation and surface area analysis, respectively (Gregg and Sing, 1999). The

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total pore volume (Vp) was quantified by converting the volume of nitrogen adsorbed at

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p/p0 ≈ 0.99 (p and p0 denote the equilibrium pressure and the saturation pressure of

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nitrogen at 77.4 K, respectively) to the volume of liquid nitrogen.

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Adsorption experiments. Sorption was studied using batch uptake experiments detailed

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in the Supporting Information S1. The adsorptive capacity was calculated from the mass

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of metaldehyde removed from solution by the sorbent per mass of carbon, as expressed in

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equation 1, where V0 and C0 were the initial volume of contaminated solution and

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concentration of contaminant, respectively, and Vt and Ct were the volume and

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concentration of contaminant in solution at a certain time. Adsorption studies were

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performed in triplicate, by incubating 20 mg of carbon in 40 ml of contaminated aqueous

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solution. When the aqueous solution was ultrapure water, the pH of the solution was 6.2.

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Adsorptive capacity: (V0C0-VtCt)/ sorbent mass

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(1)

Water contaminated with metaldehyde was also purified by filtration through a column

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packed with phenolic carbon beads. The adsorption capacity at different points of the

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breakthrough curve was quantified by subtracting the area below the breakthrough curve,

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expressed in mass of metaldehyde units, from the mass of metaldehyde filtered through

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the column at a given filtrate volume. The levels of metaldehyde contamination assayed

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in this work, with the exception of the isotherm study, were significantly higher than

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environmental levels (1µg/L), in order to compare the carbons at their maximum

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adsorptive capacity and also to allow observation of breakthrough using realistic volumes

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of spiked water (i.e. within 6000 bed volumes) during filtration studies.

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Analysis of metaldehyde Methaldehyde and d5-atrazine, used as an internal standard,

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were analysed via LC-MS as described in the Supporting Information S2. The limit of

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detection for metaldehyde was 0.1 µg/L. Surface water samples, untreated and treated

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with carbon, were analysed by standard addition consisting of additional 3 non-spiked

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and 5 spiked levels. Before injection into the LC, sample extracts were diluted in

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methanol (60%) and centrifuged (10 min at 16.000 rpm) to precipitate macromolecules

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that could adsorb in the chromatographic column and affect the ionization in the MS

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ionisation source.

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Statistical methods. Statistical comparison of the uptake of metaldehyde from spiked

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ultrapure water by phenolic carbons with different physico-chemical properties (inter-

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treatments/intra-water) and the application of the optimal carbon in the treatment of water

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from different sources spiked with metaldehyde (intra-treatment/ inter-water) was

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performed using one-way ANOVA tests (P 0.05). Comparison between the adsorption of

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metaldehyde spiked into different types of water using GAC or the optimal phenolic

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carbon was carried out using a two-way ANOVA test with replicates (P 0.05).

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Regression analysis was carried out to establish the correlation between the SBET of the

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phenolic carbons and the uptake of metadehyde under the same experimental conditions.

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A two-sided t test was carried out to assess the correlation between the two assessed

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variables. Microsoft Excel software was used throughout for statistical analyses.

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3. RESULTS AND DISCUSSION

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Effect of degree of activation on metaldehyde adsorption. The chemical structure of

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the small cyclic ether which constitutes the metaldehyde molecule explains part of the

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difficulty associated with its removal from water. Being a polar molecule with short

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hydrocarbon structure implies relatively low affinity with activated carbon; previous

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studies report adsorptive capacities of 0.4mg metaldehyde/ g carbon for activated

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charcoal (Shintani et al., 1999), and up to one hundred times higher for potassium

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hydroxide-activated powder activated carbon (PAC) (Gessner and Hasan, 1987). PAC is

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not a technology that can easily be applied in waste water treatment plants (WWTPs) due

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to its small particle size, and granular activated carbon is the adsorbent currently used.

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Since active surface is a key parameter in adsorption processes (McNaught and

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Wilkinson, 1997), especially in physisorption where the forces involved (van der Waals

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type) are not strong, the adsorption of metaldehyde should be enhanced by using carbons

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with higher active surface area. To test the effect of active surface area and maximise the

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adsorption of metaldehyde, carbons with a range of activation degrees, and hence surface

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areas, were synthesised and tested at equilibrium conditions. The results, expressed in

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various standard units, are shown in Figure 1. As expected, increasing the degree of

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activation caused an increase of surface area and total pore volume, and consequently a

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decrease in the bulk density (Figure 1). Notably however an increase in surface area did

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not increase the adsorption capacity of metaldehyde (P 0.05).

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Metaldehyde has an approximate area of 214.9 Å2. At the working conditions of the study

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(40 ml of metaldehyde spiked in water at 62 mg/L, incubated with 20 mg of carbon, S1),

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the total number of molecules of metaldehyde in the initial solution was 8.48·1018, which

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would cover a total of 18.2 m2 of carbon surface. Each of the incubations was carried out

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with 20 mg of carbon, therefore, when comparing the carbons from low to high activation

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degree, there was 20.8 m2 of carbon surface covered with metaldehyde, assuming a

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monolayer, when using the carbon with SBET 1041 m2/g; 28.6 m2 in the carbon with SBET

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1432 m2/g and 40.36 m2 in the carbon with SBET 2018 m2/g. After the incubations, which

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were carried out until equilibria, the same amount of metaldehyde was left in solution

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despite the increase of active surface and the fact that these phenolic carbons were not

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saturated. A test for correlation showed that SBET and the adsorption capacity for

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metaldehyde were not correlated, with r2 = 0.592; t experimental and critical values for

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the two-sided t test were 1.70 and 4.30, respectively (P 0.05), which supports the null

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hypothesis of no correlation between the two parameters. Furthermore, a negative

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correlation between adsorptive capacity and SBET was found when the results were

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expressed in terms of pore volume (r2=0.9998). Therefore, although initial activation is

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desirable since it removes amorphous carbon deposits from pores and therefore improves

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pore availability, further activation has negligible effect on the adsorption of

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metaldehyde. This indicates that a more complex process is governing the uptake of

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metaldehyde than simple surface physisorption.

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Effect of pore size distribution and particle size on metaldehyde adsorption. In a

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scenario where a molecule does not adsorb on the carbon surface by simple

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physisorption, as shown above by the lack of positive correlation between the increase in

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SBET and metaldehyde adsorption, pore-contaminant interactions may be key controls on

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contaminant removal. To examine the role of pore size and pore size distribution on

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metaldehyde adsorption, six different carbon samples where microporosity was

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predominant were tested for batch uptake of metaldehyde. Two microporous phenolic

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carbons (M1 and M2) with differences in particle size and slight differences in SBET and

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pore volume (Vp) were synthesised by the authors and compared with the performance of

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four carbon samples from three different providers, described in section 2, under batch

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conditions. The carbon structure was characterised via liquid nitrogen adsorption

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porosimetry and data are provided in Table 2 and in Supporting Information S3. The

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carbons studied could be separated into 2 groups based on pore size distribution; Ceca

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cpw, Norit CGP super and Picapure HP120 8/15 were nano/mesoporous and M1, M2 and

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Picatiff EPII were just nanoporous, with a narrow distribution of pores below 25Å.

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Despite the differences in porosity, all the carbons tested had similar SBET: 1400 ±186

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m2/g. Batch uptake results for metaldehyde (Table 2) indicate that variations in the pore

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size distribution influence metaldehyde uptake, with higher adsorption capacities

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obtained for samples with narrower pore size distribution in the micropore range. The

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increase of surface area did not increase the adsorption capacity, confirming earlier data.

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To further examine metaldehyde adsorption processes in these carbons, kinetic studies

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were undertaken using high concentrations of metaldehyde (51 mg/L) (Supporting

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Information S1, Figure 2). The carbons assayed had different particle sizes but similar

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SBET, approximately 1188m2/g, and pore volume V1.0 0.51 cm3/g, because the

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microporosity is the main contributor to the active surface available in this type of porous

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material, and the particle size represents only a relatively small contribution to it. The

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smallest carbon beads (<45µm) exhibited the fastest uptake of metaldehyde and

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equilibrium was reached within 10 minutes. For beads with intermediate particle size (45-

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125µm), equilibrium was reached after 6h, while 24h were required for the largest beads

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(210-250µm) to achieve the maximum adsorption of metaldehyde. Since surface area has

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been found not to influence the adsorption of metaldehyde, the more rapid uptake of

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metaldehyde at smaller particle sizes can be attributed to the higher accessibility (and

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shorter bulk transfer/ diffusion pathways) of the micropores located near the particle

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surface. Similar results were observed under equilibrium conditions using lower

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concentrations of metaldehyde (0.8 mg/L), where the microporous carbons with smaller

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particle size (< 45 µm) outperformed the larger ones (210-250 µm), with adsorptive

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capacities of 1.3 ± 0.1 and 1.1 ± 0.03 mg metaldehyde/g carbon respectively, difference

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in performance that could be attributed to differences in pore structure.

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Effect of Point of Zero Charge (PZC) on metaldehyde adsorption. The PZC indicates

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under which pH conditions the density charge of a surface is zero. This property can

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influence the attraction of substances in solution to the carbonaceous surface and

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variations in PZC can be achieved by controlling the atmosphere during carbon activation

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and the presence of oxidizing agents in solution leading to generation of carboxylic acid,

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hydroxyl and other groups that provide ion exchange properties (Teixidó et al., 2011; Ni

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et al., 2011). In the literature, carbon with surface modifications towards higher surface

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polarity, achieved by increasing the number of oxygen acidic groups (low PZC) have

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been used for the removal of metallic ions, and nitrogenated carbon (with high PZC) for

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the removal of species that are neutral or negatively charged at typical environmental pH

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such as phenol, cyanide or atrazine (for a review see Rivera-Utrilla et. al., 2011).

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Phenolic carbon beads, with micro and mesoporosity (TE3), covering a range of PZC

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have been synthesised and tested for the adsorption of metaldehyde, and performance is

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shown in Figure 3. The carbons with high PZC values showed higher uptake of

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metaldehyde. These carbons are predominantly positively charged for a broad range of

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pH (via protonated carboxylic acids and basic functional groups) below the PZC.

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Moreover, it was found that the adsorptive capacities of the carbons with the three

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highest PZC, expressed in terms of pore volume, were highly correlated with PZC

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(r2=0.999). Lower correlation was found when the adsorption was expressed in terms of

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mass of the carbon (r2=0.971). Carbons with low PZC will stay negatively charged at

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environmental pH and the lower uptake of metaldehyde observed compared to high PZC

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values (Figure 3) may be due to water solvatation of the charged sites predominating over

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the interaction with metaldehyde.

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Effect of surface modification on metaldehyde adsorption. The effect of PZC on

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metaldehyde uptake could be influenced by the nature of the functional groups providing

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the charge. Hence, carbon beads with different acidic and basic group functionality but

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similar structural features among the carbons were synthesised. The synthesis of these

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carbons is described in the Materials and Methods section. Briefly, carbon “TE3”, the

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starting material presented 0.58 mmol/g of combined carboxylic functions (mainly free

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carboxylic acid, anhydride, lactone, lactole) as determined by back titration after reaction

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with Na2CO3; and total acidic functionalities of 1.16 mmol/g as determined by back

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titration after reaction with NaOH via Boehm titration (Valente and Carrot, 2006). Hence,

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the phenolic OH content was 0.58 mmol/g. TE3 was oxidised to “TE3 ox”, carbon with

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0.82 meq/g carboxylic acids, 0.11 meq/g carboxylic acid derivatives and 0.77 meq/g

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phenolic hydroxyls on the surface according to the characterisation via Boehm titration

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(Valente and Carrot, 2006). “TE3 ox” was derivatised with ethyldiamine “TE3-EN” and

333

N,N dimethylethyldiamine “TE3-Me2EN”. In addition, phenolic carbon with slightly

334

bigger mesopores and a higher number of micropores, TE7, was modified with sulphonic

335

acid groups at 2 different concentrations on the surface. Additional structural information

336

on TE3 and TE7 carbons is given in the Supporting Information S4. The adsorption of

337

metaldehyde by the range of carbons with surface modifications is shown in Figure 4,

338

where the uptake of metaldehyde is expressed in terms of mass of carbon and pore

339

volume. It can be seen that surface modification leading to positive and negative surface

340

charge caused a reduction in adsorption of metaldehyde, and the starting carbon, (carbon

341

“TE3”), showed the highest adsorption. These results are in agreement with the data

342

found in section 3.3 where neutral or positively charged surfaces were found to favour

343

the adsorption of metaldehyde. In this case, the results reveal that high positive charge

344

density may not enhance the adsorption, possibly because metaldehyde competes with

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water to solvate these charged sites. The carbon sample with the highest amount of

346

sulphonic groups and larger transport pores showed good performance, with a removal of

347

69.4 ± 0.1 mg metaldehyde/g. This removal is probably due to the degradation of

348

metaldehyde at the acidic sites.

349

Optimisation of the size of the transport pores and comparison with GAC. In general

350

terms, the higher the amount of pore former used in the carbon synthesis, the wider the

351

mesopores, up to macropores, and the higher the pore volume. In addition, higher

352

activation degrees result in higher numbers of micropores, slightly broader meso and

353

macropores and less dense carbons. Carbon beads synthesised with different amount of

354

pore former, polyethyleneglycol in this case, and activation degree were prepared to

355

obtain markedly different porous structure and have been assayed for the removal of

356

metaldehyde compared to GAC. The carbon beads were TE3 (slightly mesoporous), TE7

357

(slightly macroporous) and TE8 (highly macroporous). The surface chemistry of both

358

TE3, TE7 and TE8 was kept constant with 0.58 mmol/g of combined carboxylic

359

functions, total acidic functionalities at 1.16 mmol/g and PZC ranging between 10.022

360

and 10.094.

361

The structural characterisation of GAC via liquid nitrogen adsorption isotherms has

362

shown an isotherm type IV, indicating dominantly microporous structure, with lower

363

pore volume than the phenolic carbons assayed (Supporting Information S4). Pores of

364

dimensions 11-20 Å were the main contributors to the surface area of the GAC sorbent.

365

Mesopores were found between 21-38 Å and macropores were not observed.

366

Based on batch incubation of an aqueous solution of metaldehyde at 64 mg/L with 30 mg

367

of each type of carbon, the removal capacity was found not to significantly differ

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368

between the phenolic resin-based carbon beads; 74.5 ± 4.23; 75.7 ± 1.14; 71.3 ± 5.34 mg

369

metaldehyde/g carbon, for TE3, TE7 and TE8, respectively. Adsorption was much lower

370

on GAC, at 12.8 ± 0.73 mg metaldehyde/g carbon. This indicates that slightly

371

mesoporous carbons, achieved with

372

indicated in Table 1 and low activation temperatures (where only 34% of carbon has been

373

lost as CO2 in the case of TE3), were enough to guarantee the diffusion of metaldehyde

374

through the interconnected porous structure leading to the micropores.

375

The adsorptive capacity achieved with the TE3, TE7 and TE8 carbon beads almost

376

doubled the uptake observed for beads where microporosity dominated (Table 2) at high

377

concentrations of metaldehyde, which may indicate that transport pores, in addition to

378

micropores, contribute to the phenomena taking place for the adsorption of metaldehyde.

379

Figure 5 shows the kinetics of adsorption on the optimal beads, in the size range 125-250

380

µm. The maximum metaldeyde uptake was reached at 30 minutes for TE7 and at 180

381

minutes for TE3, showing once more that transport pores, which are more abundant in

382

TE7, are beneficial for the kinetics of adsorption.

383

Performance of optimised carbon (TE7)

384

A comparison between the performance of TE7, tailored for the removal of metaldehyde,

385

and GAC has been carried out by incubating the carbons with metaldehyde-spiked

386

aqueous solutions until equilibria at a range of concentrations which cover realistic

387

environmental levels (1 µg/L) to high concentrations that would only take place in the

388

case of spillages (58 mg/L). The experimental data conform to a Langmuir model both

389

for TE7 (r2= 0.994) and for GAC (r2=0.997).

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the amount of pore former added to the resin

17

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The Langmuir model considers the coverage of the sorbent with a monolayer of sorbate.

391

Langmuir-type isotherms rise steeply from the origin and form a plateau with a well-

392

marked knee, which is the case for the isotherm obtained for metaldehyde (Figure 6). If a

393

further rise occurred, it might have been caused by a re-orientation of the sorbate or the

394

formation of a second adsorbed layer, but this behaviour has not been observed here.

395

Moreover, the slope of the curve in a Langmuir model is related to the so called

396

“Langmuir adsorption constant” which increases with the binding energy of adsorption.

397

Therefore, it can be distinguished that the adsorption of metaldehyde is much stronger in

398

the phenolic carbon than in GAC by comparing the slope of the curve obtained for TE7

399

and GAC.

400

The removal of metaldehyde was also tested in through flow mode (Figure 7), a mode

401

that involves kinetic and thermodynamic components in the adsorption and is useful for

402

upscaling purposes. The concentration of metaldehyde in the contaminated feed solution

403

(0.5 mg/L) was selected to be higher than environmentally realistic levels by a thousand

404

times, in order to be able to measure the break through point within a week of filtration.

405

Under the conditions specified in Figure 7, the adsorption capacity was 6.9 , 10.0 and

406

11.4 mg metaldehyde/g carbon at the last safe filtrate (i.e. below the 0.1µg/ L limit); at

407

the inflexion point of the curve; and at the limit of saturation, respectively. Over 3000

408

bed volumes of contaminated water were treated before breakthrough. The capacity of

409

the optimal carbon beads to remove metaldehyde was maintained in environmental

410

(surface water) samples spiked at 5 mg metaldehyde/L, as shown in Figure 8. The

411

samples tested included river water (Ouse River (Sussex, UK) taken from “Spatham

412

Lane” (freshwater tributary) and the Ouse estuary in Newhaven harbour (saline sample),

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18

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water from a lake (Balcombe) and water from a reservoir (Ardingly) located in close

414

proximity with Balcombe Lake (Sussex, UK). The performance of the carbons in these

415

different surface water samples was also compared to tap (i.e. standard drinking) water

416

(Brighton) and ultrapure water. This study was carried out in batch mode. Specifically,

417

the characteristics of the waters used were: ultrapure water (pH 6.2, TOC 0.036 mg/L);

418

tap water (pH 7.9, TOC 3.61 mg/L); Balcombe (lake) (pH 7.8 ,TOC 6.22 mg/L);

419

Ardingly (drinking water reservoir) (pH 8.1, TOC 7.65 mg/L); Ouse river (Spatham lane)

420

(pH 8.3, TOC 10.28 mg/L); and Ouse river (Newhaven) (pH 8.1, TOC 6.73 mg/L). The

421

latter sample contained high total dissolved salts, with Na+ 9320 mg/L; K+ 514 mg/L,

422

Mg2+ 1261 mg/L; Ca2+ 339 mg/L as major ions.

423

Comparison between the adsorption of metaldehyde spiked into different types of

424

environmental waters using GAC and the optimal phenolic carbon was carried out using

425

two one-way ANOVA tests and a two-way ANOVA test with replicates (P 0.05). The

426

results from the one-way ANOVA test using GAC indicated that the performance of

427

GAC was statistically similar for all types of water, with the exception of the sample

428

obtained from Newhaven harbour (the sample with the highest salinity and hence a very

429

high concentration of dissolved ions). The same test was used for TE7, and similar uptake

430

of metaldehyde was found between the spiked water samples, with the exception of the

431

spiked ultrapure water and water from Newhaven harbour. The two-way ANOVA

432

revealed that the type of carbon (GAC or TE7) affected the uptake of metaldehyde

433

significantly (F experimental=951.561, and F critical value =4.260) whereas the type of

434

water did not (F experimental=1.629, F critical=2.621). A significant interaction between

435

the type of water and carbon used (F experimental 5.659, F critical 2.620) was found.

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In all cases, phenolic carbon was shown to be highly efficient for the removal of

437

metaldehyde, despite high levels of TOC (up to 10.28 mg/L), changes in pH (6.2 - 8.3)

438

and strong differences in salinity, outperforming GAC in every case. The data indicate

439

that the porous synthetic carbons do not “clog” or block despite high levels of organic

440

matter in the raw surface water, nor are they highly affected by potentially competing

441

substances from the water source. This may be an effect of the porous “skin” of the

442

carbons, which may limit the diffusion of large molecules, and possibly the presence of

443

selective sites which show some degree of selectivity for the adsorption of metaldeyde

444

compared to other potential competing molecules and ions present in these waters.

445

Indeed, the uptake of metaldehyde in these surface water was statistically similar in all

446

surface water samples (P 0.05), with exception of the estuarine water, most likely due to

447

the very high salinity of that water (around marine salinity). These results underline the

448

potential for these phenolic resin-derived carbons to be used for effective metaldehyde

449

removal in environmentally-realistic situations, as an addition or replacement to

450

conventional GAC treatment. Based on experimental data, the “tailored” structure of

451

these carbons (i.e. high microporosity with presence of mesopores to facilitate diffusive

452

transport) is a significant factor in enhancing the adsorption of metaldehyde compared to

453

conventional activated carbons. The high attrition resistance of the carbons makes them

454

appropriate for water treatment applications although their smaller particle size compared

455

to standard GAC implies that further adaptation of the carbons may be required to enable

456

their use in GAC-based treatment plant. Pilot upscaling tests are currently ongoing in

457

collaboration with the UK water industry.

458

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4. CONCLUSIONS

20

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459

•

Phenolic resin-derived activated carbons with optimised structure and surface chemistry have been found to be highly effective for metaldehyde removal in

461

environmentally-realistic situations in comparison to GAC currently used in

462

tertiary water treatment.

463

•

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460

The adsorptive capacity for metaldehyde is not linked to active surface area. Adsorption is favoured in carbons with high microporosity with narrow pore size

465

distribution, although the presence of mesopores are important in allowing

466

effective diffusive transport of metaldehyde to active sorption sites. Surface

467

modification of the carbon causes a reduction in adsorption capacity, due to

468

possible competitive effects between metaldehyde and water molecules. •

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464

Under maximum adsorption conditions, when treating water heavily contaminated with metaldehyde (64 mg metaldehyde/L) the uptake obtained was 76 mg

471

metaldehyde/g carbon in the “designer” phenolic carbon compared with 13 mg

472

metaldehyde/g carbon in industrial GAC. Adsorption isotherms carried out to

473

model the adsorption of metaldehyde at a range of contamination levels, including

474

environmentally-realistic levels, showed higher adsorption and capacity of the

475

phenolic carbons with respect to GAC at all concentration levels.

477 478 479

EP

•

The adsorption of metaldehyde by the phenolic carbons, in contrast to GAC, was

AC C

476

TE D

470

maintained even in the presence of high concentrations of organic matter (and

inorganic salts), indicating the potential utility of these “designer” carbons in

waste and/or drinking water treatment.

480 481

ACKNOWLEDGEMENTS

21

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The authors thank the EC Seventh Framework Programme Marie Curie Actions, the

483

Industry-Academia Partnership and Pathways Scheme (Carbosorb, project no. 230676)

484

and the Intra European Fellowship (Polarclean, project no. 274985), for financial support.

485

Prof. S.V. Mikhalovsky is acknowledged for useful and informative discussions. Dr

486

Howard Dodd, C. English, S. Kumar, Y Zheng are acknowledged for their technical

487

support. Two anonymous reviewers are acknowledged for their comments and

488

suggestions, which improved the overall quality of this paper.

SC

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482

489

Table 1. Solution composition for the synthesis of phenolic carbon beads with tailored

491

porosity. EG = Ethylene Glycol.

M AN U

490

492

Resin solution composition Novolac, Hexamine, EG, weight weight parts weight parts parts 10 1.5 11.5 10 2 18

Meso- or macropore size, A 300-400

10

800-1000

TE D

Type of porosity in the carbon beads microporous micromesoporous micromacroporous

2

EP

493

30

494

Table 2 Removal of metaldehyde using microporous carbon expressed per units of

496

surface, mass and volume. The range of particle sizes for the phenolic carbons M1 and

497

M2 was 210-250µm, and 45-125 µm, respectively. The four external carbons were PAC

498

of size 8-15 µm. The starting concentration of metaldehyde used in contact with the

499

carbon was 50 mg·L-1.

AC C

495

500 501 Carbon name

Structural features

Adsorptive capacity

22

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mg metaldehyde/

mg metaldehyde/

mg metaldehyde/

(cm /g)

2

m ±s

g carbon±s

cm3porevolume±s

1166

0.49

0.033±0.002

38.4 ±2.2

M2

1188

0.51

0.034±0.002

40.6 ±2.4

78.4±6.3 79.7±4.8

P1icactiff EPII

1400

0.61

0.027±0.001

37.6 ±1.0

48.6±1.7

Ceca cpw

1495

1.32

0.014±0.001

20.7 ±2.2

15.7±1.7

Norit-CGP super

1548

1.18

0.012±0.001

18.9 ±2.5

16.0±2.1

Picapure HP120 8/15

1606

1.16

0.016±0.002

25.9 ±2.5

22.3±2.2

2

(m /g) M1

Vp 3

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SBET

504

SC

502 503 FIGURE CAPTIONS

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505 506

Figure 1. Effect of the activation degree, surface area and pore volume on the uptake of

507

metaldehyde (n=3) from ultrapure water spiked with metaldehyde (62 mg/L). Adsorption

508

condition are given in Materials and Methods section and S1.

509

Figure 2. Effect of particle size on the adsorption kinetics of metaldehyde by

511

microporous carbons, with similar SBET. Adsorption condition are given in Materials

512

and Methods section and S1.

EP

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510

513

Figure 3. Effect of PZC on the uptake of metaldehyde, expressed in terms of sorbent

515

mass and pore volume (n=6). The starting concentration of metaldehyde was 50 mg

516

metaldehyde·L-1. Adsorption condition are given in Materials and Methods section and

517

S1.

AC C

514

518 519

Figure 4. Effect of surface derivatisation on the removal of metaldehyde. Phenolic carbon

520

(TE3), was oxidised (TE3 ox), and derivatised with ehtylenediamine (TE3-EN), N,N 23

ACCEPTED MANUSCRIPT

521

dimethylethyldiamine “TE3-Me2EN” and

sulphonic groups “TE3-SO3” The initial

522

concentration of metaldehyde was 40 mg/L. Adsorption condition are given in Materials

523

and Methods section and S1.

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524

Figure 5. Kinetic study on the impact of transport pores on the adsorption of

526

metaldehyde. See text for discussion of characteristics of TE7, TE3 and GAC. The error

527

bars are hidden by the marker in some of the data points. Adsorption condition are given

528

in Materials and Methods section and S1.

M AN U

529

SC

525

Figure 6. Adsorption isotherms for the removal of metaldehyde by TE7 and GAC. The

531

parameters (a,b) show the adjustment of the experimental data to the Langmuir model.

532

The error bars are hidden by the marker in some of the data points. Adsorption condition

533

are given in Materials and Methods section and S1.

534

TE D

530

Figure 7. Breakthrough curve obtained when filtering ultrapure water spiked with

536

metaldehyde at 0.5 mg/L through a column (5 mm i.d, 70 mm) packed with TE7 carbon

537

(0.3223g) at 0.38 ml/min and 25 ºC.

AC C

538

EP

535

539

Figure 8. Comparison between the performance of GAC and the mesoporous phenolic

540

carbon TE7 in the removal of spiked metaldehyde added to surface water samples from

541

the area of East Sussex, UK. For ease of reading, metaldehyde concentrations after

542

treatment with TE7 are also shown multiplied by 10. The error bars correspond to

24

ACCEPTED MANUSCRIPT

543

standard deviation obtained from the addition standard calibration. The batch study was

544

carried out for 48h in an orbital shaker (at 90 rpm) at 25 ºC.

545

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546 547 548

SC

549 REFERENCES

551

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552

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555 556

Bonton, A., Bouchard, C., Barbeau, B., Jedrzejak, S., 2012. Comparative life cycle

557

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EP

558

Bristol Water, UK, 2012. Briefing on metaldehyde [online] Available from:

560

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AC C

559

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582

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586

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595

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Kozynchenko, O. P., Strelko V.V., Blackburn A.J., Tennison S.R. 2002. Porous carbons.

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Salame, I. I., Bandosz, T. J., 1999. Study of water adsorption on activated carbons with

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TE D

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Seredych, M., Bandosz, T. J., 2008. Role of microporosity and nitrogen functionality on

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the surface of activated carbon in the process of desulfurization of digester gas. The

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626

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Shintani, S., Goto, K., Endo, Y., Iwamoto, C., Ohata, K., 1999. Adsorption effects of

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mesoporous and microporous activated carbons by immobilization of diamine. Journal of

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639

the ionizable antibiotic sulfamethazine on black carbon (Biochar). Environmental

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Tennison, S. R., Tunbridge, J.R., Place, R.N., Kozynchenko, O. 2008. Making discrete

643

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The metaldehyde stewardship group, 2013. Promoting responsible metaldehyde

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647

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648

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649

TE D

645

Valente Nabais, J. M., Carrott, P. J. M., 2006. Chemical characterization of activated

651

carbon fibers and activated carbons. Journal of Chemical Education 83 (3), 436-438.

652

AC C

650

653

Wang, X., Liu, R., Waje, M. M., Chen, Z., Yan, Y., Bozhilov, K. N., Feng, P., 2007.

654

Sulfonated ordered mesoporous carbon as a stable and highly active protonic acid

655

Catalyst. Chemistry of Materials 19 (10), 2395-2397.

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658

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659

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660

(Accessed November 2013).

RI PT

657

661

Water UK, 2013. Water UK briefing paper on metaldehyde [online] Available from:

663

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664

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662

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665 666

Zhongguo, X. X., Chong B. F., Zhi Z.Z., 2013. Molluscicidal effect and cost-

667

effectiveness of suspension concentrate of metaldehyde and niclosamide in the field in

668

Honghu City. Chinese journal of schistosomiasis control 25(3), 320-321.

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Pore volume (x10)

60

Surface Area (m2/g)

1500

M AN U

50 40

1000

20 10 0 GAC

EP

TE D

30

Non activated

2000

500

0 29 % activation

Type of carbon

47 % activation

65 % activation

Surface Area (m2/g)

70

RI PT

Adsorptive capacity (mg metaldehyde/g C)

SC

80

AC C

Adsorptive capacity (mg metaldehyde /g C) and Vp (cm3/g C)

Figure 1. Effect of the activation degree, surface area and pore volume on the uptake of metaldehyde (n=3) from ultrapure water spiked with metaldehyde (62 mg/L). Adsorption condition are given in Materials and Methods section and S1.

ACCEPTED MANUSCRIPT

Bead size <45 μm

mg metaldehyde/g C

60 50 40

Figure 2 Effect of particle size on the adsorption kinetics of metaldehyde by microporous carbons, with similar SBET. Adsorption condition are given in Materials and Methods section and S1.

20 10 0

1000

2000 time (min)

3000

Bead size 45-125 μm

mg metaldehyde/g C

50 40 30 20 10 0

0

mg metaldehyde/g C

AC C

EP

TE D

M AN U

60

SC

0

RI PT

30

1000

2000 time (min)

3000

Bead size 210-250 μm

60 50 40 30 20 10 0 0

1000

2000 time (min)

3000

ACCEPTED MANUSCRIPT

SC

50

30

EP

20

0

1000

TE D

40

1500

10.058

TE3

9.615

500

Surface Area (m2/g)

60

10

2000

M AN U

70

AC C

Adsorptive capacity (mg metaldehyde/g C) Adsorptive capacity (mg metaldehyde/cm3 and pore volume (cm3/g C)

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Figure 3 Effect of PZC on the uptake of metaldehyde, expressed in terms of sorbent mass and pore volume (n=6). The starting concentration of metaldehyde was 50 mg metaldehyde·L-1. Adsorption condition are given in Materials and Methods section and S1.

8.743

2.297

0 TE3 with higher activation

Type of Carbon

TE3 impregnated with urea

TE3 oxidised

Adsorptive capacity (mg metaldehyde/g C) Pore volume (x10) Adsorptive capacity (mg metaldehyde/cm3) PZC Surface Area (m2/g)

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mg metaldehyd/cm3 C

50

TE D

40

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60

mg metaldehyd/g C

30

EP

20 10 0 TE3

AC C

Adsorptive capacity (mg metaldehyde/ g carbon)

70

SC

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Figure 4 Effect of surface derivatisation on the removal of metaldehyde. Phenolic carbon (TE3), was oxidised (TE3 ox), and derivatised with ehtylenediamine (TE3-EN), N,N dimethylethyldiamine “TE3-Me2EN” and sulphonic groups “TE3-SO3” The initial concentration of metaldehyde was 40 mg/L. Adsorption condition are given in Materials and Methods section and S1.

TE3 ox

TE3-EN

Type of carbon

TE3- Me2EN

TE7-SO3H TE7-SO3H (0.27 mmol/g C) (0.59 mmol/g C )

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80

20 50 0 0

500

1000

1500

2000

2500

3000

250

300

350

400

TE D

40

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40

60

TE7 TE3 GAC

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60

70

30

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20 10

0 0

50

AC C

Mealdehyde left in solution (mg /L)

80

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Figure 5. Kinetic study on the impact of transport pores on the adsorption of metaldehyde. See text for discussion of characteristics of TE7, TE3 and GAC. The error bars are hidden by the marker in some of the data points. Adsorption condition are given in Materials and Methods section and S1.

100

150

200

Contact time (min)

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Figure 6. Adsorption isotherms for the removal of metaldehyde by TE7 and GAC. The parameters (a,b) show the adjustment of the experimental data to the Langmuir model. The error bars are hidden by the marker in some of the data points. Adsorption condition are given in Materials and Methods section and S1.

Metaldehyde adsorption isotherms on phenolic carbon (TE7) and GAC

SC M AN U

70

y=

60

40

EP

30 20

1+·b·x TE7

b

a

TE D

50

a·b·x

TE7 97.27 GAC 14.96

0.25 0.041

GAC

AC C

Adsorption of metaldehyde onto carbon (mg metaldehyde/ g carbon)

80

10 0 0

5

10

15

20

25

30

35

40

45

50

55

Metaldehyde equilibrium concentration (mg/L)

60

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Figure 7 Breakthrough curve obtained when filtering ultrapure water spiked with metaldehyde at 0.5 mg/L through a column (5 mm i.d, 70 mm) packed with TE7 carbon (0.3223g) at 0.38 ml/min and 25 °C.

0.6

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0.5 mg metaldehyde/L

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0.4

EP

TE D

0.3

0.2

AC C

Metaldehyde (mg/L)

0.5

0.1

<0.1 μg metaldehyde/L 0 0

1000

2000

3000

Bed volume

4000

5000

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Figure 8 Comparison between the performance of GAC and the mesoporous phenolic carbon TE7 in the removal of spiked metaldehyde added to surface water samples from the area of East Sussex, UK. For ease of reading, metaldehyde concentrations after treatment with TE7 are also shown multiplied by 10. The error bars correspond to standard deviation obtained from the addition standard calibration. The batch study was carried out for 48h in an orbital shaker (at 90 rpm) at 25 °C.

SC M AN U

6.00 5.00

TE D

4.00

EP

3.00 2.00

AC C

Concentration of metaldehyde (mg/L)

7.00

1.00 0.00 Ultrapure water

Tap water

Balcombe lake

Ardingly reservoir

Metaldehyde initial concentration

Spatham lane (river) After treatment with GAC

Ouse (New Haven) river

After treatment with TE7

Amplification (x10) of the treatment with TE7

ACCEPTED MANUSCRIPT HIGHLIGHTS

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• •

Current water treatment cannot remove metaldehyde, a common molluscicide We examine designer phenolic carbons that have high capacity for metaldehyde removal The internal structure and surface charge of the carbon is key to its performance. Adsorption capacity is maintained even in complex environmental media

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• •

ACCEPTED MANUSCRIPT Water Research

Phenolic carbon tailored for the removal of polar organic contaminants: a solution to

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the metaldehyde problem?

1

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R. Busquets1,2,3, O.P. Kozynchenko2, R. L. D Whitby3, Steve Tennison2, Andrew B. Cundy1*

School of Environment and Technology and 3School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton, BN2 4GJ. United Kingdom.

MAST Carbon International Ltd. Jays Close Basingstoke, Hampshire RG22 4BA, UK

3

Kingston University, Faculty of Science, Engineering and Computing, Kingston Upon

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2

AC C

EP

Thames, KT1 2EE, UK

Corresponding author phone: +44 (0)1273642270; e-mail: [email protected]. University of Brighton S1

ACCEPTED MANUSCRIPT 5 PAGES TABLE OF CONTENTS S1. Experimental conditions in the adsorption tests

S3. Nitrogen isotherms of microporous carbons

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S2. LC-MS conditions for the determination of metaldehyde

AC C

EP

TE D

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S4. Structural properties of the phenolic carbons TE3, TE7, TE8 and GAC.

S2

ACCEPTED MANUSCRIPT Supporting information S1. Adsorption tests. Adsorption tests were carried out in batch mode under equilibrium conditions using an orbital shaker model SI500 (Stuart Scientific, UK) at 90 rpm, 25 ºC for

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48h, unless otherwise indicated. To assess the performance of sorbents that presented very high adsorptive capacity it was necessary to filter highly contaminated water to detect metaldehyde left in solution above 0.05 µg metaldehyde/L, our detection limit. To avoid precipitation of metaldehyde, 2% ethanol was used to stabilise the contaminants in aqueous

SC

solution and prevent their precipitation, which would cause overestimation of the adsorption

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capacity of the sorbents tested.

The adsorption test for kinetic studies were carried out as follows. Aliquots (0.25 ml) were periodically taken from the supernatant and analysed for metaldehyde. A total of 2 out of 40 ml where withdrawn for analysis during the study; a set of incubations was employed to

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study short analysis time (up to 360min) and another set for the period (from 720 min). The study was carried out in triplicate. The adsorption was carried in an orbital shaker (90 rpm) at

EP

25 ºC.

AC C

S2. Analysis of metaldehyde by LC-MS. Stock solutions of metaldehyde and d5-atrazine were prepared at 1 mg/ml with methanol and used for further dilutions. Standard mixtures containing metaldehyde, at concentrations ranging between 0.3 µg/L and 0.5 mg/L, and d5atrazine as an internal standard at a constant concentration of 0.11 mg/L were prepared by weight for the calibration curves. Metaldehyde was analysed using an LC system model Series 1100 from Agilent Technologies (USA) coupled to an ion trap mass spectrometer model HCT Esquire (Bruker Daltonik GmbH) equipped with an off-axis electrospray working in positive mode. The separation was carried out by fast chromatography using an S3

ACCEPTED MANUSCRIPT Ascentis express fused core C18 column with 2.7 µm particle size, 100 mm × 2.1mm I.D (Sigma-Aldrich GmbH) at a flow rate of 0.25 ml/min in isocratic conditions; 65% methanol in water at 40 ºC. The optimal conditions of the electrospray were nebuliser gas (N2) 55 psi, dry gas (N2) 12 L/min and 360 ºC as dry temperature. The optimal potential applied in the ion

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optics were capillary -4500V; end plate offset -500V; skimmer 15.0V; capillary exit 95.1V; octapole 1 DC 18.38V; octapole 2 DC 1.84V; octapole RF 107.4 V; lens 1, -5.8V; and lens 2, -72V. The determination was carried out in full scan (scan range 150-400 mass-to-charge

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ratio (m/z)), using an adduct of metaldehyde with sodium, with 199 m/z, for quantification. Metaldehyde was fragmented with 1.0 V amplitude and the product ion 155 m/z, which

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corresponds to the loss of acetaldehyde, was used as a confirmation. When working at concentrations above 0.01 mg/L, the injection volume was 5 µl, conditions that provided a limit of detection for metaldehyde, defined as a signal-to-noise ratio of 3, of 0.6 µg/L. Higher injection volume, 30 µl, was used for the analysis of aqueous solutions where metaldehyde

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was at concentrations lower than 0.01 mg/L, giving limits of detection of 0.05 µg/L.

S.3. Nitrogen isotherms, specific surface area (SBET) and total pore volume (V0.99) of

EP

microporous carbons synthesised in this work (M1, M2) and industrially activated carbon

AC C

powders: Picactiff EPII 8/15, coded as PA, PICAPURE HP 120 8/15, coded as PP; CECA CPW, coded as C, and Norit CGP Super, coded as NS

S4

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N2 isotherms of microporous phenolic carbons synthetised in this work

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N2 isotherms of microporous from external PAC 900

900 M1 M2

PP

SBET = 1166 m2/g; V 0.99= 0.49 cc/g

700

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700

TE D

400

SBET = 1400 m2/g; V 0.99= 0.61 cc/g

400

EP

Vol. Ads. (cc

SBET = 1548 m2/g; V 0.99= 1.18 cc/g SBET = 1495 m2/g; V 0.99= 1.32 cc/g

500

500

300

300

AC C

Adds. Vol. (cc/g)

PA

600

600

\

C

SBET = 1606 m2/g; V 0.99= 1.16 cc/g

SBET = 1188 m2/g; V 0.99= 0.51 cc/g

g)

NS

SC

800

800

200

100

200

100

0

0 0

0.2

0.4

0.6

P\Po

0.8

1

0

0.2

0.4

0.6

P\Po

0.8

1

S6

ACCEPTED MANUSCRIPT S4 structural properties of the phenolic carbons TE3, TE7, TE8 and GAC. Structural features Vp

(m2/g)

(cm3/g)

TE3

1057

1.14

TE7

1703

1.65

TE8

2018

1.86

GAC

552

1.04

AC C

EP

TE D

M AN U

SC

SBET

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Carbon name

S7