Removal of Pesticides and Volatile Organic Pollutants With Nanoparticles

CHAPTER 13

Removal of Pesticides and Volatile Organic Pollutants With Nanoparticles Vicente de Oliveira Sousa Neto1, Paulo de Tarso Cavalcante Freire2 and Ronaldo Ferreira do Nascimento3 1

Laboratory of Study and Research of Pollutant Removal by Adsorption (LERPAD), Department of Chemistry, State University of Ceara´ (UECE-FECLESC), Quixada´, Brazil 2Department of Physics, Federal University of Ceara, Fortaleza, Brazil 3Laboratory of Trace Analysis (LAT), Department of Analytical and Physical Chemistry Chemistry, Federal University of Ceara´-UFC, Fortaleza, Brazil

13.1 Introduction Air pollution has a negative impact on the ecosystem as well as for human health. It affects the life of a society. According to the World Health Organization (2018), outdoor air pollution in cities and rural areas was responsible for 4.2 million deaths worldwide in 2016. Taken together, indoor and outdoor air pollution caused an estimated 7 million deaths, or one in eight deaths, globally in 2016 (WHO, 2018). The pollutants released into the air environment are in different forms such as toxic gases (nitrogen oxides, sulfur oxides, carbon oxides, ozone, etc.), suspended particulate matter (PM), and volatile organic compounds (VOCs). From a health perspective, these forms are more important. Nanomaterials have some important properties such as large specific surface areas, size distribution, molecular structure, hydrophilicity/lipophilicity, and high reactivity. All these physicochemical characteristics make nanomaterials suitable for a wide range of environmental applications such as adsorbents, catalysts, and sensors. Some nanotechnology applications have already been developed. For polluted-air treatment, many researchers focus on toxic-gas nanosensors, nanofilters for materials particulate (MPs), and nanoporous titanium dioxide film in a photocatalytic unit to remove VOCs and degrade residual ozone (Khan et al., 2014; Das et al., 2015). In general, nanotechnology can be applied in air-pollution control through three major categories: (1) remediation and treatment; (2) detection and sensing; and (3) pollution prevention (Sofian et al., 2012; Yadav et al., 2017). Nanomaterials Applications for Environmental Matrices. DOI: https://doi.org/10.1016/B978-0-12-814829-7.00013-6 © 2019 Elsevier Inc. All rights reserved.

405

406 Chapter 13 In this chapter, the application of nanotechnology to combat air pollution through sensors, monitoring, and degradation techniques will be discussed.

13.2 Air Remediation Using Nanosize Particles 13.2.1 Nanostructured Photocatalysts In the past few years, many scientific projects have dedicated attention to the application of photodegradation, through a semiconductor, to eliminate organic molecules which are harmful to people’s health. According to the fundamental principle of semiconductors, at a sufficient level of light the charge transfer process will occur from the valence band to the conduction band causing the surrounding substance to be oxidized. Semiconductor photocatalysts can be modified (or supported in nanomaterials) in terms of reactivity and selectivity to be more efficient. There are many oxides that have been successfully applied as photocatalysts, such as titanium dioxide (TiO2), zinc oxide (ZnO), iron (III) oxide (Fe2O3), and tungsten oxide (WO3). In their nanostructured form, these oxides are more efficient. TiO2 is one of the most effective photoinduced catalysts. This oxide is commonly used to oxidize organic and inorganic compounds in air and water due to its high oxidative capacity and long-term photostability. Other advantages of TiO2 is that it is a low-cost and nontoxic material. Fig. 13.1 shows a proposal for a primary process for preparing TiO2 using semiconductor photocatalysis. It is noted that through UV irradiation (λ , 380 nm) on the TiO2 surface an electron is promoted from the valence band to the conduction band (with a band gap energy of 3.2 eV), leaving a positive hole behind. (Binas et al., 2017) In this way, TiO2 particles act as electron donors or acceptors for molecules reaching its surface.

Figure 13.1 Primary processes for preparing TiO2 in semiconductor photocatalysis. Reproduced with permission from Binas et al., 2017.

Removal of Pesticides and Volatile Organic Pollutants With Nanoparticles 407 Positive holes and electrons participate in redox reactions on the surface of the semiconductor with water, oxygen, and adsorbed organic or inorganic compounds leading to the mineralization of the pollutants. Wu and van der Krol (2012) proposed a new strategy to change the photocatalytic selectivity of nanosized TiO2. In that paper, the authors reported on the creation of a large and stable concentration of oxygen vacancies via iron (Fe) doping (Fig. 13.2). The researchers confirmed that this process results in the photoreduction of NO to N2 and O2 and that the photooxidation reaction can be largely suppressed. According to the authors, while efficiency was still modest, the Fe/TiO2 photocatalyst did not show any signs of deactivation. Energy demand for alternative fuels associated with low CO2 emissions has stimulated the search for CO2 reducers in the production of clean fuels such as ethanol, methanol, methane, and H2. (Fig. 13.3). However, because CO2 is a chemically stable compound, its conversion to carbon-based fuels requires a substantial amount of energy. Therefore solar energy has been a viable strategy to meet the demand for energy. The challenge is to improve energy conversion efficiency to make the photocatalysis process economically viable. First it is necessary to develop photocatalysts that are more active under a more expanded light spectrum and, thus, a more effective use of radiant energy is possible.

Figure 13.2 Photoreduction reaction by doping TiO2 nanoparticles with Fe. This figure by Vicente Neto is licensed under the Creative Commons Attribution 4.0 International License.

408 Chapter 13

Figure 13.3 Schematic of visible light-induced CO2 photoreduction. Reproduced with permission from Ola et al., 2015. This article is available under the terms of the Creative Commons Attribution License (CC BY).

Photoreduction of CO2 is a promising method to improve atmospheric levels of this harmful gas. TiO2 for use in visible-light applications have been modified by metal/or oxide metal doping and this procedure modifies the electronic properties of TiO2 making it capable of increasing the efficiency and selectivity of the product for CO2 photoreduction. The metal/ metal oxide, additionally, has its own catalytic activities and bandwidth reduction (Ola and Maroto-Valer, 2015). Ola and Maroto-Valer (2015) obtained transition metal oxide-based TiO2 nanoparticles via the sol
gel method for visible light-induced CO2 photoreduction (Fig. 13.4). According to the authors, the introduction of these metal ions into the host framework not only modified the crystallinity of TiO2, but also were able to influence its light-absorption properties. They studied V-, Cr-, and Co-TiO2 photocatalysts immobilized onto quartz plates. The results showed that the photoconversion rates were remarkably enhanced by the metal-doped TiO2 supports when compared to pure TiO2. It was noted that the Co-TiO2 sample had the highest photoconversion rates. They also concluded that experimental results obtained from the sol
gel-derived M
TiO2-based supports could be further optimized to improve CO2 reduction efficiency for future applications. Organic compounds in indoor air can be removed via the photocatalytic oxidation method which is able to convert organic pollutants (e.g., VOCs, dioxins, PCBs) in the air into

Removal of Pesticides and Volatile Organic Pollutants With Nanoparticles 409

Figure 13.4 Schematic of sol
gel procedure. Reproduced with permission from Ola et al., 2015. This article is available under the terms of the Creative Commons Attribution License (CC BY).

benign and odorless constituents such as water vapor (H2O) and CO2. Wang et al. (2006) investigated the role of a potential promoter (ZrO2) in enhancing a visible-light photocatalyst (TiO2-xNx) for the oxidation of gaseous organic compounds. According to the authors, nitrogen-doped photocatalysts were obtained by reacting amorphous metal oxide xerogels with an ammonia solution (37%), followed by calcination of the products at 600 C
400 C for 4 hours. This synthesis method avoids the use of toxic NH3 gas in the nitridation step which use ammonia solution. Fig. 13.5 shows a flowchart of some VOC removal techniques (Khan and Goshal, 2000). According to Mo et al. (2009), when organic compounds are chemically transformed by a photocatalytic oxidation (PO) device, it is the hydroxyl radical (OH ) derived from the oxidation of adsorbed water or adsorbed OH2 that is the dominant oxidant. Its net reaction with a VOC can be expressed as: TiO2 1 hv-h1 1 e2

(13.1)

OH 1 VOC 1 O2 -nCO2 1 H2 O

(13.2)



410 Chapter 13 VOC removal techniques

Process and equipment modification

Add on control techniques

Recovery

Destruction

Bio filtration

Oxidation

Absortption

Thermal oxidation

Catalytic oxidation

Adsorption

Condensation

Membrane separation

RFR

Zeolite based adsorption

Activated carbon-based adsorption

Figure 13.5 Classification of VOC control techniques. Reproduced with permission from Khan and Goshal, 2000.

In reaction Eq. (13.1), h1 and e2 are powerful oxidizing and reducing agents, respectively. The reactions that are established in the nanoparticle surface are given in Eqs. (13.3) and (13.4).  Oxidation reaction: h1 1 OH2 -OH (13.3) Reduction reaction: e2 1 O2ðadsÞ -O2 2ðadsÞ

(13.4)

Fig. 13.6 shows that VOC removal by photocatalytic oxidation (PCO) is a surface-reaction process. There are two important steps: first, the VOCs have to be transferred to the reaction surface; and second, the VOCs are decomposed by the photocatalyst. The reaction surface area is the most important performance parameter of a PCO device. Xie et al. (2018) used pure SnO2 for the photocatalytic abatement of water pollutants. However, it did not show good performance probably due to its large band gap which only allowed about 5% UV light in solar energy to be utilized by SnO2. Some methods for improving SnO2 photocatalytic ability have been reported which involves increasing its surface area by preparing porous SnO2 (Manjula et al., 2012) and/or decreasing SnO2 particle sizes (Bhattacharjee and Ahmaruzzaman, 2015).

Removal of Pesticides and Volatile Organic Pollutants With Nanoparticles 411

Figure 13.6 Reactions established on the nanoparticle surface. Reproduced with permission from Mo et al., 2009.

Figure 13.7 Unit cell of the K-OMS-2 crystal structure: representation with (A) octahedral sites; and (B) explicit atoms (the atom in the center represents K; the big spheres represent Mn; and the small spheres represent O). Reproduced with permission from Genuino et al., 2018.

Manganese Oxide Octahedral Molecular Sieves (OMS-2) is a manganese oxide with K 1 cation occupying the tunnel structure formed by sharing corner and edge of MnO 6 octahedra (Fig. 13.7). Recently, OMS-2 and metal ion doped OMS-2 were documented to show effective photothermocatalytic activity for VOC abatement under UV
Vis
IR and Vis
IR illumination due to their high thermocatalytic activity and effective photothermal conversion in the whole solar spectra, see Fig. 13.8 (Hou et al., 2015; Chen et al. 2018). In order to improve photocatalytic activity of SnO2, Xie et al. (2018) studied the synergetic

412 Chapter 13

Figure 13.8 UV photocatalysis on SnO2, photoactivation and light-driven thermocatalysis on OMS-2, and synergetic effect. Reproduced with permission from Xie et al., 2018.

photothermocatalysis
photocatalysis effect for organic air pollutant abatement using OMS-2/SnO2 nanocomposites. According to the authors, the thermocatalytic activity of pure SnO2 is quite low and only exhibits thermocatalytic activity from temperatures above 260 C. This result suggests that good thermocatalytic activity of OMS-2/SnO2 can be primarily ascribed to the thermocatalytic oxidation of benzene on OMS-2.

13.2.2 Gas Nanosensor and Detectors Gas-sensing studies aim to create an electronic “nose” that can detect each kind of gas is present in ambient atmosphere at low concentration levels, with sufficient sensitivity, selectivity, and reproducibility (Fig. 13.9). Semiconductor nanostructured metal oxides have been widely used in various fields such as photodetectors, photocatalysts, dye-sensitized solar cells, and light emitting diodes (LED). These properties are due their large surface-to-volume ratio, excellent thermal stability, and low tendency to form aggregates. They also have potential application as gas sensors due to their porous network that allows the rapid diffusion of gases to the entire surface which enables a high-gas response and a short-response time. Another advantage of the porous network structure is the possibility of uniform doping and loading of catalytic materials on the sensor’s surface. In semiconductors, wide-band gap n-types, such as SnO2 (Li et al., 2017), ZnO (Kim et al., 2018), In2O3 (Wang et al., 2018), and WO3

Removal of Pesticides and Volatile Organic Pollutants With Nanoparticles 413

Figure 13.9 Diagram of a gas-sensing characterization system. Reproduced with permission from Sun et al., 2018. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

(Qin et al., 2017) have been prepared in different forms to explore their potential for gas-sensor applications. ZnO Nanostructured /or based nanostructures: ZnO is also a commonly used semiconductor photocatalyst due to its high photosensitivity, photochemical stability, large band gap, strong oxidizing power, and nontoxic nature. The successful application of ZnO requires the development of techniques for improving its physicochemical properties by controlling their size, morphology, and structural and surface characteristics, as well as efforts to enhance their photochemical response to visible/solar light. SnO2: Tin dioxide is a common metal oxide gas-sensing material. SnO2 gas sensors can react with the electrons of the gas which are bound by the adsorbed oxygen. In this process, the electrical resistance change is derived from the interaction of adsorbed oxygen with combustible gases at approximately 250 C
350 C. SnO2 gas sensors have been successfully applied in commercial gas-alarm systems, airquality sensors, odor sensors, and alcohol monitors for human breath. These sensors detect combustible gases such as hydrogen, carbon monoxide, and ethanol vapors by a change in electrical resistance. The gas detection mechanism of SnO2 gas sensors is based on the reaction of adsorbed oxygen with combustible gases on the surface.

414 Chapter 13 O2ðgÞ 1 2e2 -2O2 ad

(13.5)

O2ðgÞ 1 4e2 -2O22 ad

(13.6)

SnO2 sensors have good response for many VOCs gases, such as methanol, ethanol, formaldehyde, acetone. (Zheng et al., 2010; Chiu et al., 2007; Du et al., 2012; Zhang et al., 2014). According to Sun et al. (2018), formaldehyde and acetone sensing processes can be described using these reactions: 2 HCHOðgÞ 1 2O2 ads -CO2ðgÞ 1 H2 OðgÞ 1 2e

(13.7)

2 CH3 COCH3ðgÞ 1 8O2 ads -3CO2ðgÞ 1 3H2 OðgÞ 1 8e

(13.8)

Karthik et al. (2016) fabricated and used (Cu)-incorporated Cu-Incorporated SnO2 nanoparticles as gas sensors for measuring CO atmospheres. Nanostructured SnO2 was synthesized by homogeneous precipitation, employing urea as the precipitant agent. Then the resultant SnO2 powder was ball milled and incorporated with a transition metal, Cu, via a chemical synthesis method. Fig. 13.10 summarizes the synthesis of both pure SnO2 and Cu:SnO2 through a flux chart. According to the authors, pellets consisting of SnO2 powder are more practical for gas sensors than thin films due to their higher porosity, surface area, and having no substrate effects. Fig. 13.11 illustrates a gas-sensing system using SnO2. Pellets consisting of SnO2 powder are highlighted. According to Karthik et al. (2016), SnO2 acts as a gas-sensing matrix and Cu acts as a structure modifier by increasing the surface reactivity with the gases. Similarly to reactions of formaldehyde and acetone sensing processes, Eqs. (13.7) and (13.8), carbon monoxide can be expressed by Eq. (13.9). 2 2COðgÞ 1 O2 ads -2CO2ðgÞ 1 e

(13.9)

Fig. 13.12 shows the typical sensor responses of pure and Cu-incorporated SnO2 composites. It is noted that Cu-incorporated pellets exhibited greater sensing responses than the pure SnO2 at all temperatures, even to very small amounts of CO (1 ppm). Fig. 13.13 (Left) shows the response and recovery times of pure SnO2 and Cu:SnO2 measured at 300 C and for 300 ppm of CO gas concentration. The graphic results suggest that the reason for the increase in the sensitivity and decrease in the response and recovery times is due to the structural and morphological changes occurring in the Cu-incorporated SnO2 powders. (Right) The gas-sensing mechanism of pure SnO2 in (a) air and (b) CO; and Cu:SnO2 pellets in (c) air and (d) CO gas-sensing concept in Cu:SnO 2 and pure SnO2 powders.

Removal of Pesticides and Volatile Organic Pollutants With Nanoparticles 415 (A) SnCI4·5H4O 0.4M 30 mL of tin chloride

SnO2

CH4N2O 0.4M

Calcination in 800ºC for 2 h in a normal atmosphere.

1:2 mixtures

60 mL of urea The resultant pastes were dried in air at 100ºC for 24 h in order to eliminate the aqueous solvents.

SnCI4·5H2O + CH4N2O The mixed solution was stirred and heated until reaching a temperature of 93 ± 5ºC

The precipitate were washed, then it was centrifuged at 400 rpm for 1 h until the pH of the supematant reched 12.

Precipitate was formed

(B) SnCI4·5H2O 0.4M

Cu:SnO2 powers

CH4N2O 0.4M

(1) Calcination in 800ºC for 2 h in a normal atmosphere.

Ball milled for 6 h at 400 rpm CuCI2 + wt% The resultant pastes were dried in air at 100ºC for 24 h in order to eliminate the aqueous solvents.

CuCI2 + SnCI4·5H2O

CuCI2 + SnCI4·5H2O + CH4N2O The mixed solution was stirred and heated until reaching a temperature of 93 ± 5ºC

The precipitate were washed, then it was centrifuged at 400 rpm for 1 h until the pH of the supematant reched 12.

Precipitate was formed

Figure 13.10 Experimental procedure for the synthesis of: (A) pure SnO2; and (B) Cu:SnO2. This figure by Vicente Neto is licensed under the Creative Commons Attribution 4.0 International license.

Karthik et al. (2016) confirmed via a detailed study that the presence of copper in the SnO2 pellets increased the conductivity and conferred further sensitivity to the CO sensor. Additionally, copper-incorporation produced better oxygen adsorption and, subsequently, decreased the response and recovery times of the sensor.

416 Chapter 13

Figure 13.11 Gas-sensing system using SnO2. Reproduced with permission from Karthik et al., 2016. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

Figure 13.12 CO sensing response of (A) pure and (B) Cu-incorporated SnO2 pellets. Reproduced with permission from Karthik et al., 2016. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

Removal of Pesticides and Volatile Organic Pollutants With Nanoparticles 417

Figure 13.13 (Left) Sensitivity, response, and recovery times of pure SnO2 and Cu:SnO2 pellets. (Right) Gassensing mechanism (Karthik et al., 2016). Reproduced with permission from Karthik et al., 2016. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

CNTs-based gas sensors: CNTs are categorized as either single-wall carbon nanotubes (SWCNTs) or multiwalled carbon nanotubes (MWCNTs). They exhibit some interesting properties as well as offering significant advantages for their application as gas sensors. These materials are known to present typical sensor properties such as extreme sensitivity to charge transfer and chemical doping effects by their interaction with various molecules. In the same way as metal oxide-based sensor materials behave, metal nanoparticles (NPs) have frequently been incorporated into CNTs to improve sensing performance (Colidres et al., 2014). Toxic gases in ambient air can also be cleaned via CNTs. Both SWNTs and MWNTs have been developed for toxic-gas removal via adsorption processes. It has been shown that they have good potential as superior adsorbents to remove various types of organic and inorganic pollutants in air streams and in aqueous environments. Its potential is linked to its onedimensional structure, thermal stability, and exceptional chemical properties. Better performance adsorption by NCTs can be implemented by the introduction of functional groups on the surface or can be achieved by modifying the chemical or thermal treatment to tune the CNTs to have optimal performance for a particular purpose.

418 Chapter 13 Wongwiriyapan et al. (2006) synthesized SWNTs, by directly growing on the sensor substrate. SWNT deposited on the sensor surface promoted better ozone sensitivity. They also reported that the new ozone-sensor device was able to detect ozone down to 6 ppb at room temperature while operating with a fast response. Park et al. (2009) developed an ozone-gas sensor using SWCNT. Their device was sensitive to ozone down to 50 ppb with rapid response and fast recovery. Kong et al. (2011) applied SWNT modified with an aminophenylamino cyclodextrin for the detection of persistent organic pollutants (POP). The phenylenediamine-β-CD/SWCNT hybrid compound formed resulted in significant variation of the electrical conductance associated with different levels of POP adsorption. According to Kong et al. (2011), SWCNTs decorated with mono-6-deoxy-6-(p-aminophenylamino)-β-cyclodextrin were applied to chemosensors for detection of POPs due to its special molecular structure, that is, a hydrophobic internal cavity and a hydrophilic external surface for molecular recognition. This structure probably can improve sensitivity and selectivity for detecting organic molecules because it is expected that an inclusion complex with guest molecules can be efficiently formed between the hybrid material and POPs, such as TCB, CD-68, aldrin, and HCB. Fig. 13.14 shows a schematic representation of the synthesis of p-phenylenediamine-β-CD/SWCNT hybrid material. According to the authors, the hybrid material behaves as an electrical sensor that is chemically specific and was capable of detecting nanomolar concentrations of TCB. Kumar et al. (2016) studied adsorption kinetics of NO2 on a SWCNT gas sensor (Fig. 13.15). NO2 belongs to a group of gases called nitrogen oxides (NOx) and forms from emissions from cars, trucks and buses, and power plants, etc. While all of these NOx gases are harmful to human health and the environment, NO2 is of greater concern because it primarily gets into the air from the burning of fuel. Kumar et al. (2016) proposed to analyze the simultaneous reversible and irreversible adsorption on the gas-sensor surface by establishing a general model. According to the authors, this model can be used for the analysis of experimental data of the response curve in sensors. By the experimental evidence, they concluded that the sensing response of NO2 increased with the increase in concentration of the analyte gas. It was also noted that the theoretical data and experimental results were agreement suggesting that the model fitted the experimental data reasonably well for all NO2 concentrations. The values of the forward rate of reaction for irreversible and reversible sites are in the range of 1.51 3 1025
3.17 3 1025 and 1.68 3 1022
9.8 3 1024 ppm21 s21 extracted from fitting data using this model. The activation energy of reversible sites lay in the range of 0.83
067 eV. It was, thus, observed that, in general, CNT-based gas sensors are able to operate at room temperature with low-power consumption. This feature is useful in hazardous applications where continuous gas monitoring is required.

Removal of Pesticides and Volatile Organic Pollutants With Nanoparticles 419

Figure 13.14 Schematic representation of synthesis of p-phenylenediamine/β-CD and preparation of Phenylenediamine-β-CD/SWCNT hybrid. This figure by Vicente Neto is licensed under the Creative Commons Attribution 4.0 International license.

13.3 Nanomembranes for Air Remediation The development of nanomembranes is another field from nanotechnology that has been applied for air-pollution control. Nanostructured membranes have pores small enough to separate different pollutants from exhaust fumes. The challenges are linked to their improvement. In general, nanomaterial fabrication is an intricate process because it involves various steps like selecting a cost-effective material for fabrication suited to the required conditions. The nanomembranes act as a molecular sieve to absorb gases. It is made with materials based on aluminosilicate compound known as zeolite and they also are used to divide the substances on a molecular stage. An air filter is considered efficient when it is able to capture a number of different air pollutants. Therefore the efficiency is associated with the type of air pollutant and

420 Chapter 13

Figure 13.15 Schematic sketch of NO2 adsorption on SWCNT gas sensor: (A) resistive gas sensor; (B) heterogeneous SWCNTs bundle with some impurity particles; and (C) A1, A2, and θ represent occupied sites by analyte molecules and empty sides on the nanotube, respectively. Reproduced with permission from Kumar et al., 2016

eventually can be tuned by the pollutant capturing mechanism. This topic will be approached specifically concerning gas nanofilters and particulate matter nanofilters both synthesized from of electrospinning technique.

13.4 Electrospinning Technique Currently there are many techniques to fabricate nanofibers. These include conjugate spinning, chemical vapor deposition, phase separation (sol
gel process), drawing, selfassembly, melt-blowing, and electrospinning (Ko and Wan, 2014). Among these, electrospinning is a versatile and widely accepted process for producing air filter media (Wang et al., 2014). Electrospinning is a technique to produce artificial textile filaments using an electric force on a polymer fluid. It is a versatile process to produce nanofibers and control their shape. Electrospun materials are suitable for air filtration due to their small-pore size and high specific-surface area. Nanofibrous mats commonly exhibit higher particle capture efficiency, but may also have a disadvantage that may affect its operational use. They certainly will lead to higher airflow resistance compared to macro-fibrous materials due to their tighter structure.

Removal of Pesticides and Volatile Organic Pollutants With Nanoparticles 421

13.4.1 Gas Filters The largest source of air pollution is from motor vehicles. Engines emit many types of pollutants including NOx, VOCs, CO, CO2, particulates, SO2, and lead. The efficiency of an air filter is related to the type of atmospheric pollutants and to the mechanism used for their capture. Basically, there are two capture mechanisms proposed to remove air pollution: physisorption and chemisorption. Nanofibers can have strong Van der Waals interaction with gaseous pollutants due to their higher surface area that increases the physiosorption capacity. Hence, fibrous filters with extremely high surface areas should be aimed at capturing gaseous pollutants. Chemisorption means converting pollutants into simpler compounds by a chemical action including catalytic or noncatalytic reduction. Chemisorption is more selective than physiosorption and can be improved by imparting surface functionality and surface-active chemistry on the fiber structure. The functionalized electrospun nanofibers may be helpful for this purpose.

13.4.2 Nanoparticles Incorporated Into Nanofibers Recently, various researchers have focused on developing nanofilters for air filtration applications via the incorporation of nanoparticles such as MgO, TiO2, Al2O3, and other oxides into nanofibers. This is due to the capacity of nanoparticles to decontaminate wide varieties of toxic gases, such as chemical contaminants, biological contaminants (viruses, bacteria), pesticides, and many more. Nanofibers as Antimicrobial Air Filters: Air filtration technology using antimicrobial nanoparticles also have been applied to remove bioaerosols. Neeta et al. (2007) reported antimicrobial (Escherichia coli and Pseudomonas aeruginosa) activity for polyvinyl chloride (PVC), cellulose acetate (CA), and polyacrylonitrile (PAN) nanofiber membranes containing Ag nanoparticles. (Sundarrajana et al., 2014). Zhu et al. (2018) explored the application of poly(vinyl alcohol)/poly(acrylic acid) (PVA-PAA) nanofiber membranes for both particulate matters (PM) filtration as well as antibacterial/antiviral activity (see Fig. 13.16). PM is the term used for a mixture of solid particles and liquid droplets found in the air. Particle pollution includes PM10 and PM2.5, being particulate matter 10 μm or less in diameter and particulate matter 2.5 μm or less in diameter, respectively (NPI). PM can be inhaled and cause serious health problems. In fact, particles less than 10 μm in diameter pose the greatest problems because they can get deep into the lungs, and some may even get into the bloodstream. According to Zhu et al. (2018) nanofiber membranes were fabricated via green electrospinning and thermal crosslinking. In order to improve filtration performance, the authors incorporated hydrophobic silica (SiO2) nanoparticles (NPs) into the PVA-PAA nanofiber membranes. The antibacterial/antiviral activity capacity was acquired through Ag doping via silver nitrate (AgNO3) into the PVA-PAA-SiO2 NPs filtration membranes and

422 Chapter 13

Figure 13.16 A schematic diagram illustrating the fabrication of PVA/PAA/SiO2-Ag NP nanofibrous membranes (A) Electrospinning step; (B) thermal crosslink 1 UV reduction; and (C) thermal crosslink reaction at 140 C. Reproduced with permission from Zhu et al., 2018.

reduction of Ag 1 to Ag nanoparticles (Ag NPs) performed via UV reduction. Fig. 13.16 shows a schematic diagram illustrating the fabrication of PVA/PAA/SiO2-Ag NPs nanofibrous membranes vis the combination of: (A) electrospinning, UV reduction, and thermal crosslinking; (B) PVA/PAA/SiO2-Ag NPs membranes application for air filtration; and (C) thermal crosslinking mechanism between PVA and PAA via esterification reaction. According to the authors, the proposed green synthesis generated fibers without toxic organic solvent, did not possess any harmful cytotoxic effects, and the membranes were produced with stable high filtration efficiency (even after being tested 150 times). The asprepared PVA-PAA-SiO2-Ag NP nanofibrous membranes exhibited high filtration efficiency for both nonoil aerosols and oil aerosols irrespective of the air aerosol flow. The incorporation of the Ag NPs bestowed the pristine PVA-PAA-SiO2 NPs nanofibrous membranes with potent antibacterial activities against both Gram-negative (E. coli) and Gram-positive bacteria (Bacillus subtilis).

Removal of Pesticides and Volatile Organic Pollutants With Nanoparticles 423

Figure 13.17 Fabrication process for high-energy TiO2 nanocrystals (HE-TiO2-NCs) decorated TiO2 nanofibers (TiO2-NFs). Reproduced with permission from Duan et al., (2018).

13.4.3 Nanofibers for the Removal of Volatile Organic Compounds Chuang et al. (2014) developed an associated method between TiO2 with the electrospinning technology. To improve the surface area of the TiO2, it was prepared using nonwoven, binding-titania nanofibers. Then, the obtained catalyst was applied to treat VOCs and reduce particulate emissions. According to the authors, the results showed that the degradation efficiency for the removal of acetone was above 99% with a light source at UV-254 nm. Although the removal efficiency of particulate matter with nanofiber decreased with increasing gas pressure, it was noted that the removal efficiency of particulate matter can be greater than 98% with nanofibers. Duan et al. (2018), reported the fabrication of novel, hierarchically structured TiO2 nanomaterials, high-energy TiO2 nanocrystals (HE-TiO2-NCs) decorated with TiO2 nanofibers (TiO2-NFs), by electrospinning cubic TiOF2 nanocrystals containing a tetrabutyl titanate (TBT) solution follow by calcination (see Fig. 13.17). According to the authors, the photoreactivity of HE-TiO2-NCs/TiO2-NFs was greatly enhanced in the oxidation of acetone and NO. This effect was ascribed to the formation of a homojunction between HE-TiO2-NCs and TiO2-NFs.

13.5 Conclusion This chapter focused on demonstrating the potential application of nanotechnology as an efficient technological tool to combat air pollution, particularly the removal of volatile organic pollutants. For this it was evidenced that the development of monitoring sensors and techniques of degradation (or removal) of toxic volatile compounds are essential in this

424 Chapter 13 process. However, depending on the physicochemical characteristics of the volatile compounds, nanomaterials are suitable (or not) for broad environmental application, mainly in the form of adsorbents, catalysts, and sensors

Acknowledgment The authors acknowledge the financial support of the following Brazilian agencies toward scientific and technological development: CNPq (Process 304888/2014-1) and BNB-FUNDECI (2017.0002), FUNCAP (P130086-00057.01.00/13), MCTI/CNPq/CT-Biotec (402835/2013-1)

References Bhattacharjee, A., Ahmaruzzaman, M., 2015. Facile synthesis of SnO2 quantum dots and its photocatalytic activity in the degradation of eosin Y dye: a green approach. Mater. Lett. 139, 418
421. Binas, V., Venieri, D., Kotzias, D., Kiriakidis, G., 2017. Modified TiO2 based photocatalysts for improved air and health quality. J. Materiomics 3, 3
16. Chiu, H.-C., Yeh, C.-S., 2007. Hydrothermal synthesis of SnO2 nanoparticles and their gas-sensing of alcohol. J. Phys. Chem. C 111, 7256
7259. Chuang, Y.-H., Hong, G.-B., Chang, C.-T., 2014. Study on particulates and volatile organic compounds removal with TiO2 nonwoven filter prepared by electrospinning. J. Air Waste Manage. Assoc. 64, 738
742. Chen, J., Li, Y.Z., Fang, S.M., Yang, Y., Zhao, X.J., 2018. UV
Vis-infrared light-driven thermocatalytic abatement of benzene on Fe doped OMS-2 nanorods enhanced by a novel photoactivation. Chem. Eng. J 332, 205
215. Colindres, S.C., Aguir, K., Cervantes Sodi, F., Vargas, L.V., Salazar, J.A.M., Febles, V.G., 2014. Ozone sensing based on palladium decorated carbon nanotubes. Sensors 14, 6806
6818. Das, S., Sen, B., Debnath, N., 2015. Recent trends in nanomaterials applications in environmental monitoring and remediation. Environ. Sci. Pollut. Res. Int. 22, 18333
18344. Du, H.-Y., Wang, J., Su, M., Yao, P., Zheng, Y., Yu, N., 2012. Formaldehyde gas sensor based on SnO2/In2O3 hetero-nanofibers by a modified double jets electrospinning process. Sens. Actuat. B Chem 166, 746
752. Duan, Y., Liang, L., Lv, K., Li, Q., Li, M., 2018. TiO2 faceted nanocrystals on the nanofibers: homojunction TiO2 based Z-scheme photocatalyst for air purification. Appl. Surf. Sci. 456, 817
826. Genuino, H.C., Seraji, M.S., Meng, Y., Valencia, D., Steven, L., Suib, S.L., 2018. Combined experimental and computational study of CO oxidation promoted by Nb in manganese oxide octahedral molecular sieves. Appl. Catal. B 163, 361
369. Hou, J.T., Li, Y.Z., Mao, M.Y., Yue, Y.Z., Greaves, G.N., Zhao, X.J., 2015. Full solar spectrum light driven thermocatalysis with extremely high efficiency on nanostructured Ce ion substituted OMS-2 catalyst for VOCs purification. Nanoscale 7, 2633
2640. Karthik, T.V.K., Olvera, M.L., Maldonado, A., Go´mez Pozos, H., 2016. CO gas sensing properties of pure and Cu-incorporated SnO2 nanoparticles: a study of Cu-induced modifications. Sensors 16, 1283. Khan, F.I., Ghoshal, A.K., 2000. Removal of volatile organic compounds from polluted air. J. Loss Prev. Process Ind. 13, 527
545. Khan, I., Farhan, M., Singh, P., Thiagarajan, P., 2014. Nanotechnology for environmental remediation. Res. J. Pharm. Biol. Chem. Sci. 5, 1916
1927. Kim, J.-H., Mirzaei, A., Woo Kim, H., Kim, S.S., 2018. Low power-consumption CO gas sensors based on Au-functionalized SnO2-ZnO core-shell nanowires. Sens. Actuat. B 267, 597
607. Ko, F.K., Wan, Y., 2014. Introduction to Nanofiber Materials. Cambridge University Press, Cambridge.

Removal of Pesticides and Volatile Organic Pollutants With Nanoparticles 425 Kong, K., Wang, J., Meng, F., Chen, X.X., Jin, Z., Li, M., et al., 2011. Novel hybridized SWNT
PCD: synthesis and host
guest inclusion for electrical sensing recognition of persistent organic pollutants. J. Mater. Chem. 21, 11109
11115. Kumar, D., Kumar, I., Chaturvedi, P., Chouksey, A., Tandon, R.P., Chaudhury, P.K., 2016. Study of simultaneous reversible and irreversible adsorption on single-walled carbon nanotube gas sensor. Mater. Chem. Phys 177, 276
282. Li, R., Chen, S., Lou, Z., Li, L., Huang, T., Song, Y., et al., 2017. Fabrication of porous SnO2 nanowires gas sensors with enhanced sensitivity. Sens. Actuat. B 252, 79
85. Manjula, P., Boppella, R., Manorama, S.V., 2012. A facile and green approach for the controlled synthesis of porous SnO2 nanospheres: application as an efficient photocatalyst and an excellent gas sensing material. ACS Appl. Mater. Interface 4, 6252
6260. Mo, J., Zhang, Y., Xu, Q., Lamson, J.J., Rongyi Zhao, R., 2009. Photocatalytic purification of volatile organic compounds in indoor air: a literature review. Atmos. Environ. 43, 2229
2246. Neeta L. Lala., Ramaseshan, R., Bojun, Li., Sundarrajan, S., Barhate, R.S., Ying-jun, L., Ramakrishna, S., 2007. Fabrication of Nanofibers with Antimicrobial Functionality used as Filters - Protection Against Bacterial Contaminants. Biotechnol. Bioeng. 97, 1357
1365. Ola, O., Maroto-Valer, M.M., 2015. Transition metal oxide based TiO2 nanoparticles for visible light induced CO2 photoreduction. Appl. Catal. A 502, 114
121. Park, Y., Dong, K.Y., Lee, J., Choi, J., Bae, G.M., Ju, B.K., 2009. Development of an ozone gas sensor using single walled carbon nanotubes. Sens. Actuat. 140, 407
411. Qin, Y., Wang, Z., Liu, D., Wang, K., 2017. Dendritic composite array of silicon nanowires/WO3 nanowires for sensitive detection of NO2 at room temperature. Mater. Lett. 207, 29
32. Sofian, I., Harwin, Y., Kurniawan, A., Adityawarman, D., Indarto, A., 2012. Nanotechnologies in water and air pollution treatment. Environ. Technol. Rev. 1 (1), 36
148. Sun, Y., Wang, J., Li, X., Du, H., Huang, Q., Wang, X., 2018. The effect of zeolite composition and grain size on gas sensing properties of SnO2/zeolite sensor. Sensors 18, 390. Sundarrajana, S., Tana, K.L., Lima, S.H., Ramakrishnab, S., 2014. Electrospun nanofibers for air filtration applications. Proc. Eng. 75, 159
163. Wang, X., Yu, J.C., Chen, Y., Wu, L., Fu, X., 2006. ZrO2-modified mesoporous nanocrystalline TiO2-xNx as efficient visible light photocatalysts. Environ. Sci. Technol. 40, 2369
2374. Wang, N., Si, Y., Wang, N., 2014. Multilevel structured polyacrylonitrile/silica nanofibrous membranes for high-performance air filtration. Sep. Purif. Technol. 126, 44
51. Wang, T., Chen, F., Ji, X., Zhang, Q., 2018. Novel Au-embedded In2O3 nanowire: synthesis and growth mechanism, Superlattices Microstruct. 122, 140
146. Wongwiriyapan, W., Honda, S., Konishi, H., Mizuta, T., kuno, T., Ito, T., et al., 2006. Ultrasensitive ozone detection using single walled carbon nanotube networks. Jpn. J. Appl. Phys. 45, 3669
3671. World Health Statistics, 2018. Monitoring Health for the SDGs, Sustainable Development Goals. ISBN 978-924-156558-5. Wu, Q., van der Krol, R., 2012. Selective photoreduction of nitric oxide to nitrogen by nanostructured TiO2 photocatalysts: role of oxygen vacancies and iron dopant. J. Am. Chem. Soc. 134 (22), 9369
9375. Xie, X., Li, Y., Yang, Y., Chen, C., Zhang, Q., 2018. UV
Vis
IR driven thermocatalytic activity of OMS-2/ SnO2 nanocomposite significantly enhanced by novel photoactivation and synergetic photocatalysisthermocatalysis. Appl. Surf. Sci. 462, 590
597. Yadav, K.K., Singh, J.K., Gupta, N., Kumar, V., 2017. A review of nanobioremediation technologies for environmental cleanup: A novel biological approach. J. Mater. Environ. Sci. 8 (2), 740
757. Zhang, W., Tian, J., Wang, Y.A., Fang, X., Huang, Y., Chen, W., et al., 2014. Single porous SnO2 microtubes templated from papilio maacki bristles: new structure towards superior gas sensing. J. Mater. Chem. A 2, 4543
4550. Zheng, W., Lu, X., Wang, W., Dong, B., Zhang, H., Wang, Z., et al., 2010. A rapidly responding sensor for methanol based on electrospun In2O3-SnO2 nanofibers. J. Am. Ceram. Soc. 93, 15
17.

426 Chapter 13 Zhu, M., Hua, D., Pan, H., Wang, F., Manshian, B., Soenen, S.J., Xiong, R., Huang, C., 2018. Green electrospun and crosslinked poly(vinyl alcohol)/poly(acrylic acid) composite membranes for antibacterial effective air filtration. J. Colloid Interface Sci. 511, 411
423.

Further Reading National Pollutant Inventory r Commonwealth of Australia, 2018. http://www.npi.gov.au/resource/ particulate-matter-pm10-and-pm25. Tang, R., Shi, Y., Hou, Z., Wei, L., 2017. Carbon nanotube-based chemiresistive sensors. Sensors 17 (4), 882.