Cu2O nanoparticles for adsorption and photocatalytic degradation of methylene blue dye from aqueous medium

Journal Pre-proof Cu2 O NANOPARTICLES FOR REMOVAL OF METHYLENE BLUE DYE FROM SOLUTION Mrunal V. Kangralkar, Vishnu A. Kangralkar, Naeemakhtar Momin, Jayappa Manjanna

PII:

S2215-1532(19)30162-X

DOI:

https://doi.org/10.1016/j.enmm.2019.100265

Reference:

ENMM 100265

To appear in:

Environmental Nanotechnology, Monitoring & Management

Received Date:

1 July 2019

Revised Date:

6 September 2019

Accepted Date:

7 October 2019

Please cite this article as: Kangralkar MV, Kangralkar VA, Momin N, Manjanna J, Cu2 O NANOPARTICLES FOR REMOVAL OF METHYLENE BLUE DYE FROM SOLUTION, Environmental Nanotechnology, Monitoring and amp; Management (2019), doi: https://doi.org/10.1016/j.enmm.2019.100265

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Cu2O NANOPARTICLES FOR REMOVAL OF METHYLENE BLUE DYE FROM SOLUTION Mrunal V. Kangralkara, Vishnu A. Kangralkarb, Naeemakhtar Momina & Jayappa Manjannaa* a b

Dept. of Chemistry, Rani Channamma University, Belagavi 591156, Karnataka JGCHS College of Pharmacy, Ghatprabha, Belagavi, Karnataka

(*Email: [email protected]; Tel. 09916584954)

Highlights

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Abstract

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Cu2O NPs are synthesized from Cu2+ and T. arjuna bark extract under microwave irradiation. Adsorption of methylene blue (MB) on Cu2O NPs in light and dark condition was 63% and 55%, respectively. MB adsorption was found to follow Langmuir and Freundlich isotherm as well as pseudo second order kinetics. Complete degradation of MB occurred due to photocatalytic effect of Cu2O NPs in UV region.

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Cu2O NPs

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Graphical abstract

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In order to treat the organic pollutants like dyes in water bodies, the environmentally benign nanoparticles are used extensively. The nanoparticles preparation by green chemistry approach is advantageous for this purpose. The Cu2O nanoparticles (Cu2O NPs) were synthesized by using Cu(NO3)2 and T. arjuna bark extract (as reducing and capping agent) under microwave irradiation. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), Fourier transform infrared analysis (FT-IR) and UV-Visible spectrophotometer. The adsorption of methylene blue in presence of light and dark condition

was studied at pH 5.2. The % of adsorption in light about 63% and in dark about 55%. The adsorption followed Langmuir isotherm, Freundlich isotherm and pseudo second order kinetics. The photo induced degradation of MB dye in presence of Cu2O NPs was also studied using photocatalytic reactor under UV irradiation (250 W). The absorption of the dye solution monitored at max = 664 nm decreased with irradiation time. Up to 98% degradation of MB occurred at pH 5.2. The degradation of MB was confirmed by HPLC and LC-MS techniques.

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Keywords: Cu2O nanoparticles, T. arjuna bark extract, methylene blue dye (MB), adsorption, photodegradation

1. Introduction Aesthetic pollution is a major concern in today’s world. Effluents coming from textile, plastic and paper industries contain dyes such as methylene blue (MB), congo red, methyl red, malachite green, rose bengal etc. Among them MB (methylthioninium chloride) is a heterocyclic aromatic chemical compound with molecular formula C16H18C1N3S. It affects biological and chemical activity of water [1,2]. MB is not biodegradable and well known toxic, mutagenic and carcinogenic dye. So its disposal from waste water is important to minimize the toxicity to aquatic life and their associated problems. Many conventional methods such as oxidation, reduction, ozonation, liquid-liquid extraction, precipitation,

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membrane filtration, ion exchange, coagulation, adsorption etc have been developed for removal of dyes from waste water [3-12].

Metal and metal oxide nanoparticles (NPs) are applicable in many fields because of their morphology and active surface. They are used in the form of nanowires, nanotubes and

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nanorods as adsorbents for removal of dyes, heavy metals and pollutants from waste water [13]. The plant extracts act as reducing agent and capping agent for metal ions. The

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biosynthesis of metal NPs like Ag using apple juice [14], Au by Zizyphus ziziphus plant leaf extract [15-16], Cu by Durenta erecta plant fruit extract [17], Fe by Psidium guajava plant

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leaf extract [18], Cu by Terminalia arjuna bark plant extract [19] and metal oxide NPs like CuO by Azadirachta indica plant leaf extract [20)], ZnO by Cassia fistula plant extract [21] etc. have been reported.

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In photocatalysis, solar energy is utilized to produce hydrogen from water splitting and this hydrogen degrades the organic pollutants. During photocatalysis, semiconductor

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material absorb light energy more than or equal to its band gap, generate electrons and holes, which gives free radicals to oxidize the substrate [22]. Cu2O is a p-type semiconductor and band gap energy is 2.4 eV [23]. Now-a-days photocatalysis is one of the important method

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for removal of dyes and heavy metals from aqueous media. Herein we report the formation of Cu2O NPs using T. arjuna bark extract under

microwave irradiation. The synthesized Cu2O NPs are stable in colloidal state at room temperature. This method is very useful as compared to chemical/ physical method since no external reducing agent, stabilizing agent and solvent entities are used. The Cu2O NPs are used for investigation of MB adsorption and degradation in aqueous solution.

Methylene Blue

2. Materials and methods Terminalia arjuna bark (dry) was collected from in and around Belagavi city (Karnataka, India). Cupric nitrate (Cu(NO3)2), methylene blue (MB) dye, sodium hydroxide (NaOH) and hydrochloric acid were used without further purification. All chemicals used in the experiments are of analytical reagent grade and deionized water is used. Microwave oven

of reactants and photodegradation of MB dye respectively.

2.1

Synthesis of Cu2O nanoparticles

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(custommade) and photocatalytic reactor (Lelesil innovative system) was used for irradiation

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10 gm of T. arjuna bark (dry) was cut into small pieces, washed with distilled water to remove dust particles and impurities.Then it was taken in a RB flask containing 100ml of distilled water and connected with condenser. Then whole assembly was subjected for

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microwave irradiation (300rv) for about 7 min to extract the phytoconstituents present in the plant matter. Then the bark extract was filtered through 0.2µm membrane filtrate in hot

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condition to remove fibrous impurities. From this stock solution 10ml was added to 50ml of 10-2 M aqueous solution of Cu(NO3)2. The blue colour of cupric nitrate changes to dark brown. The mixture was irradiated in microwave oven for different interval of time. The

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colour of solution was brick red. So complete reduction of Cu(NO3)2 solution takes place within 5 min, as no colour change takes place even after further heating. The formation of

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Cu2O NPs was recorded by using UV-Vis absorption spectroscopy. The absorption value of SPR peak observed at 272 nm. After 2 min, there was no further increase in absorption and there was no colour change in reaction mixture. Finally the Cu2O nanoparticles were washed

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repeatedly with distilled water and dried in a vacuum oven at 700C for about 12 h to obtain the product in powdered form [19]. Cu(NO3)2.5H2O + T. arjuna bark extract  Cu2O NPs Synthesized Cu2O NPs by microwave irradiation method was characterized by XRD technique with Cu Kα radiation. FT-IR spectra in KBr pellet was recorded by using Thermo Scientific Nicolet iS5 spectrometer.

2.2

Adsorption and photocatalytic experiments

The removal of MB from aqueous solution by adsorption depends on the amount of adsorbent, time & pH. The effect of these parameters was studied on MB dye by using Cu2O NPs. The adsorption of MB on Cu2O NPs was carried out at room temperature (at normal condition) and in the dark and at natural pH 5.2. Approximately 20 mg of adsorbent was added in 200 ml of 1.5610-2 M MB solution and stirred at about 250 rpm by magnetic stirrer and the recording time was started after mixing the catalyst to the dye solution. After predetermined interval of time, 5ml of aliquot was taken by 10 ml syringe and centrifuges to remove catalyst particles. The concentration of MB was estimated by using UV-Visible

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spectrophotometer (UV-1800-SHIMADZU UV spectrophotometer). The absorption peaks of MB was at 292 nm and 664 nm. Furthermore the pH of dye solution was adjusted to desired value by 0.1 M NaOH or 0.1 M HCl.

The amount of MB adsorbed was calculated from following equation 𝑉

𝑞 = (𝐶0 − 𝐶𝑒 ) 𝑚

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where q is amount of dye adsorbed/unit weight of Cu2O NPs (mg/g)

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C0 ‒ initial concentration of MB (mg/L)

V ‒ volume of solution(L)

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Ce ‒ concentration of MB in solution at equilibrium time (mg/L)

m ‒ is weight of Cu2O NPs (mg) (𝐶0 −𝐶𝑖 )×100 𝐶0

2

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% 𝑎𝑑𝑠𝑜𝑟𝑝𝑡𝑖𝑜𝑛 =

Where C0 and Ci are the initial and final concentrations of MB solution.

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The photocatalytic experiment was carried out in a photochemical reactor, set with UV lamp (250 W) which emit UV radiation. 1000 ml of 1.56 ×10-2 M MB dye solution containing 100

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mg Cu2O NPs was irradiated under UV light at different reaction time up to 2 h. Before going to irradiation, the suspension was stirred in the dark for about 30 min to achieve adsorption/desorption equilibrium. The photoreactor has 1000 ml solution capacity with double jacket cylinder. The temperature of the reactor was controlled by circulating water around it. The photoreactor was set 30 cm away from the lamp. The irradiation was supplied by using UV bulb (250W). Then the suspension irradiated for UV light of photocatalytic reactor. After regular interval of time, 5ml solution of suspension was taken out, centrifused

and degradation of dye recorded by UV-Vis absorption spectroscopy. The photodegradation rate for each experiment is calculated by using following equation. % 𝑜𝑓 𝑝ℎ𝑜𝑡𝑜𝑑𝑒𝑔𝑟𝑎𝑑𝑡𝑖𝑜𝑛 = (𝐶0−𝐶𝐶𝑖)×100

3

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The efficiency of Cu2O NPs was examined by using the textile dye MB. In dark the adsorption capacity was small i.e. 16 h as compared into light was 10 h because of weak interaction of MB and Cu2O NPs. So photocatalytic reactor was used for degradation of MB dye. It is well known technique to degrade pollutants of environment. The absorption peaks of MB exhibited at 292 nm and 664 nm i.e. in UV and visible region respectively. The peak in UV region is because of absorption of the - transition with benzene ring, while peak in

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visible region is due to absorption of n- transition with –N=N− group in the MB dye molecule. 3. 3.1

Results and Discussion Formation of Cu2O NPs

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Figure 1 shows the photograph of T.arjuna bark and at right side (A) T.arjuna bark extract, (B) 10 mM Cupric nitrate solution, (C) mixture of (A) and (B) after microwave

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irradiation. The bark (dry) was cut into small pieces and washed with distilled water to remove dust particles on it. The mixture of Cu(NO3)2 solution and bark extract was dark

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brown in colour, but on microwave irradiation upto 8 min it becomes brick red colour. This implies reduction of Cu2+ to Cu+1 (Cu2O) nanoparticles. Synthesized Cu+1 nanoparticles washed with distilled water and heated in vacuum at 700c for about 12 h so as to collect Cu2O

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nanoparticles in powder form.

Figure 2 shows UV-Visible spectra of T. arjuna bark extract, cupric nitrate and Cu2O NPs. Inset shows the formation of Cu2O NPs during the irradiation of reaction mixture. The

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absorption peak maximum was at 272 nm. This peak may be due to an excitation of the surface plasmion vibration in the Cu2O nanoparticles [24].

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Figure 3 shows XRD pattern of Cu2O nanoparticles and inset shows the FT-IR spectra

of Cu2O nanoparticles (b) before and (a) after adsorption of MB. In XRD, the peaks with 2θ values of 29.60, 36.521, 42.552, 61.59 and 73.892 correspond to crystal planes of (110), (111), (200), (220) and (311) respectively of crystal Cu2O [25]. The crystallite sizes can be estimated using scherrer’s formula D =k / cosθ where the constant k is taken to be 0.94,  is the wavelength of X–ray, and  and θ are half width of peak and half of the Bragg angle

respectively. Using the equation the crystallite sizes were found to be in the range of 30-50 nm. In FT-IR, the absorption peaks are located mainly at 3461 cm-1, 1613 cm-1, 1384 cm-1 and 625 cm-1. The peak at 3461 cm-1 is the characteristic band of hydrogen bonded OH group present in aqueous solution. The peaks at 1613 cm-1 (asymmetric) and 1384 cm-1 (symmetric) and the peak at 625 cm-1 indicates Cu-O vibration of Cu2O NPs. After adsorption, significant decrease in intensities of peak of Cu2O NPs as MB dye gets adsorbed on it. The intensities of vibration band between 1700 and 1100 cm-1 of MB dye was decreased in presence of TiO2 NPs was reported [26]. Adsorption kinetics

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3.2

3.2.1 Effect of contact time

The effect of time for the removal of MB as shown in Figure 4. The Percentage adsorption (left) and adsorption capacity (right) of MB by Cu2O NPs in dark and light

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condition was shown. In dark, adsorption rate was slow and about 55% MB is removed while in light (at normal condition) it was about 63%. The change in rate of adsorption is fast

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because initially all the adsorbent sites are vacant, solute concentration gradient is very high. After some time, rate of adsorption is low because the decrease in number of vacant sites of adsorbent and dye concentration. The decreased adsorption rate indicates the possible

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monolayer formation of MB on adsorbent surface. So that the lack of available active sites

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required for further uptake after attaining the equilibrium [27].

3.2.2 Effect of pH

The pH of the solutions was adjusted to the desired level with 0.1M NaOH or 0.1M

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HCl solutions. pH of the solution was determined by using digital pH meter. The pH values were adjusted to 2, 3, 5, 7, 9 and 10 at room temperature. The pH effect on adsorption was

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studied by using 10 mg of Cu2O NPs in 100 ml of 5 ppm MB dye solution. The adsorption capacity was maximum at pH 10 as shown in Figure 5. The basic dye gives positively charged ions when dissolved in water. Thus in acidic medium availability of protons is more, the positively charged surface of sorbent tends to oppose the adsorption of cationic adsorbate. When pH of dye solution is increased the surface acquires a negative charge, thereby resulting in an increased adsorption of MB due to an increase in the electrostatic attraction between positively charged dye and negatively charged adsorbent [25,28]. 3.3

Adsorption isotherms

3.3.1 Langmuir isotherm To study the adsorption capacity of Cu2O NPs on MB, Langmuir isotherm was monitored in presence of dark and light at RT as shown in Figure 6. Langmuir model was theoretical construct. In it only a formation of monolayer on the outer surface of adsorbent i.e. no further stacking of adsorption takes place. Thus Langmuir model is equilibrium distribution of metal ions between solid and liquid phase [29]. Langmur model is proper for monolayer adsorption on a surface and is expressed as, 𝐶𝑒

𝑞𝑒 = 𝑞𝑚 𝐾𝐿 . 1+𝐾

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𝐿 𝐶𝑒

qm and KL are the constants of Langmuir equation

1 𝑞𝑒

1

=𝑞 +𝑞 𝑚

1

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The linear form of Langmuir isotherm is 5

𝑚𝐾𝐿 𝐶𝑒

Where Ce is the equilibrium concentration (mg/L), qe the amount of MB adsorbed (mg/g), qm

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is the maximum quantity of adsorption (mg/g), KL is sorption equilibrium constant (L/mg) [30]. The values of qm and KL were calculated from slope and intercept of Langmuir plot of

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1/qe versus 1/Ce. as shown in Table 1. 3.3.2 Freundlich isotherm

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Freundlich isotherm was monitored in presence of dark and light at RT as shown in Figure 7. Freunlich isotherm is applicable for heterogeneous surface of an adsorbent [29] and also used for monolayer and multilayer. The Freundlich isotherm equation expressed as, 𝑞𝑒 = 𝐾𝐹 𝐶𝑒 1/𝑛

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6

where KF = Freundlich isotherm constant (mg/g)

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n = adsorption intensity

Ce = the equilibrium concentration of adsorbate (mg/L)

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qe = the amount of metal adsorbed per gram of the adsorbent at equilibrium (mg/g) [30]. The linear form of Freundlich isotherm is 1

𝑙𝑛 𝑞𝑒 = 𝑙𝑛 𝐾𝐹 + 𝑛 𝑙𝑛 𝐶𝑒

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The values of n and KF calculated from plot of ln qe versus ln Ce as shown in Table 1.

The pseudo-second order equation is expressed as

𝑑𝑞𝑡 𝑑𝑡

= 𝐾(𝑞𝑒 − 𝑞𝑡 )2

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where qe is the amount of metal ion sorbed at equilibrium (mg/g), qt is the amount of metal ion sorbed at time t (mg/g),and k is the rate constant of the pseudo-second order kinetic model of adsorption(g/mg min). In Figure 8 the plot of t/qt versus t is straight line, from which qe and k can be determined from the slope and the intercept of the line as shown in Table 2.

3.4

Photodegradation of MB

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Before studying the photocatalytic activity of Cu2O NPs on MB dye in photocatalytic reactor, it was found that MB dye without Cu2O NPs shows negligible degradation. But in presence of Cu2O NPs it shows 97% of degradation as shown in Figure 9, UV-Vis spectra of MB and Cu2O NPs in photocatalytic reactor after irradiation at different time and inset shows the % degradation curve.

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The linear fit of MB by Cu2O NP as shown in Figure 10. It is the plot of ln (C0/Ct) vs irradiation time of photodegradtion of MB.

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The pH of 1.56×10-2 M dye solution of MB was 5. 0.1 g of Cu2O NPs added to 1 L of dye solution and then irradiated with UV lamp (250W) of photocatalytic rector. The decolourisation of dyes is familiar in literature survey .The hydroxyl radicals (OH) released in reaction which acts as oxidant, deposited on Cu2O NPs. The water molecule from the surface of NPs reacts with holes (h+(VB)) and forms hydroxyl ion radicals as shown in degradation mechanism. These hydroxyl ion radicals degrade the MB dye [31]. As the time goes, the intensity of absorption peak of MB decreases and reached to minimum level. The degradation of MB was taking place within 120 min. The % of degradation of MB was about 97%. The pH of this degraded suspension was 3.47. Mechanism of photodegradation

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Cu2O + h  e‒(CB) (Cu2O) + h+(VB) (Cu2O)

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e‒(CB) Cu2O + H2O2 •OH + ‒OH h+VB (Cu2O) + ‒OH •OH MB +.•OH  Degradation product The schematic presentation of adsorption and photocatalytic degradation of MB on Cu2O NPs in presence of light (at normal condition) and in UV light is shown in figure 11. The degraded MB was analysed by HPLC and LC-MS technique. 3.4.1 HPLC and LCMS result

The High performance liquid chromatography and mass spectrometry results of methylene blue was recorded initially and after 120 min degradation. In HPLC it was carried out at three different wavelengths. For this, C18 column (250 mm×4.6 mm, 5µm) was used in which mobile phase was 0.34% phosphoric acid (adjusted to pH 3 with triethylamine) acetonitrile (77:23) and flow rate was 1.0ml min-1. This experimental data implies that methylene blue solution after 120 min was degraded, as the peak intensity of MB was decreased. That is new photocatalytic degraded product was formed. MB shows maximum absorption (max) at 664 nm in visible region. Standard and degraded sample of Methylene Blue when subjected to HPLC, the

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results are as shown in Figure 12. The wavelength 668 nm, 246 nmand 292 nm were selected for studies [32]. At 668 nm standard MB peak has maximum absorption and its retention time was 8.542 min and area was about 4384499 respectively while for degraded sample of MB it was same retention time i.e. 8.546 min but area was about 36662 and dimer was formed.

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From that we concluded that MB was degraded. Similarly for wavelength 246 nm for standard MB retention time and peak area was 8.446 min and 1254392 respectively but for

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degraded MB it was about 8.467 min and 1149. For 292 nm wavelength retention time and peak area for standard MB, it was about 8.574 min and 1928501 respectively but for

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degraded MB it was about 8.635 min and 18044 respectively. From LC-MS (Liquid chromatography–Mass spectroscopy) the standard sample and degraded sample of MB were analysed. From Figure 13 it is clear that the prominent peak is

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at 319.9 which is molecular weight of MB dye. In it no signals of reaction transitional. But from Figure 14, after 120 min the reaction intermediates were formed when MB dye solution mixed with Cu2O NPs, analyzed by LC-MS i.e. the structure of MB dye was disturbed [33-

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36]. The intensity of degraded MB peak is so much decreased as compared to standard MB

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peak intensity.

The degradation mechanism of MB

N N

N (H3C)2N

(H3C)2N

N(CH3)2

S

(H3C)2N

N(CH3)2

S

H2N NHCH3 M/Z = 83

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HS

N

HS

NH2

(H3C)2N

M/Z = 141

M/Z = 112

NHCH3

M/Z = 268

M/Z = 284

Cl M.W = 319.85

S

S

NH2

M/Z = 241

CONCLUSION

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The Cu2O NPs synthesized by using plant extract under microwave irradiation can be used for removal of methylene blue (MB) from aqueous solution. From kinetic study, adsorption follow Langmuir and Freundlich isotherm model and pseudo second order kinetic model.

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In photocatalytic reactor MB was decolorized and degraded by green synthesized Cu2O NPs at room temperature within 2 h and percentage degradation was about 97%. The degraded products were analysed by using HPLC and LCMS method.

Acknowledgement:

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Authors greatly acknowledge financial support from the Board of Research in Nuclear Sciences (BRNS), 37 (2)/14/20/2015/ BRNS, Dt: 27/07/2015, Dept. of Atomic Energy (DAE), and DST-FIST, Ministry of Science and Technology [SR/FST/CSI-273/2016], Govt. of India.

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solutions using an acid activated Algerian bentonite: Equilibrium and kinetic studies, International Renewable Energy Congress, Sousse, Tunisia, 5–7 November 2010.

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28) H-Y. Zhu, Y-Q. Fu, R. Jiang, J.H. jiang, L. Xiao, Adsorption removal of Congo red onto magnetic cellulose/Fe3O4/activated carbon composite, Chem Eng J. 173 (2011) 494−502.

29) A. O. Dada, A.P. Olalekan, A.M. Olatunya, O. Dada, Langmuir, Freundlich, Temkin and Dubinin−Radushkevich isotherm studies of equilibrium sorption of Zn2+ unto phosphoric acid modified rice husk, IOSR J. Appl. Chem. 3 (2012) 38−45.

30) M.S. Khalili, K. Zare, O. Moradi, M. Sillanppa, Preparation and characterisation of MWCNT-COOH-cellulose-MgO NP composite as adsorbent for removal of methylene blue from aqueous solutions: isotherm, thermodynamic and kinetic studies, J. Nanostructure Chem. 8 (2018) 103−121. 31) L. Khezami, K.K. Taha, I. Ghiloufi, L.E. Mir, Adsorption and photocatalytic degradation of malachite green by vanadium doped zinc oxide nanoparticles, Water Sci. Technol. 73(4) (2016) 881−889. 32) M. Rauf, M. Meetani, A. Khaleel, A. Ahmed, Photocatalytic degradation of Methylene

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Blue using a mixed catalyst and product analysis by LC/MS, Chem. Eng. J. 157 (2010) 373−378.

33) X. Wang, L. Mei, X. Xing, L. Liao, Mechanism and process of methylene blue degradation by maganese oxides under microwave irradiation, Appl. Catal. B. 160-161

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34) T. Sinha, M. Ahmaruzzaman, Green synthesis of copper nanoparticles for efficient

pp. DOI 10.1007/s11356-015-5223-y.

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removal (degradation) of dye from aqueous phase, Environ. Sci. Pollut. Res. 2015; x, pp-

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35) A. Houas, H. Lachheb, M. Ksibi, E. Elaloui, Photocatalytic degradation pathway of Methylene blue in water, Appl. Catal. B. 31 (2001) 145−157.

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36) T. Sinha, M. Ahmaruzzaman, Photocatalytic decomposition behaviour and reaction pathway of organic compounds using Cu nanoparticles synthesized via green route,

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Photochem. Photobiol. Sci. 15 (2016) 1272−1281.

A

B

C

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Figure1 Photograph of T.arjuna plant and its bark (right) in the form of cut specimens and (A) T.arjuna bark extract, (B) 10mM Cupric nitrate, (C) mixture of (A) and (B) after

1.25 2.5

A.bark ext.

0.50

0.25

0.00

1.5 1.0

0 1 2 3 4 5 6 7 8

min min min min min min min min min

0.5

0.0 250

Cu(NO3)2 300

na

250

Absorbance

0.75

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2.0

Cu2O NPs

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Absorbance

1.00

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microwave irradiation.

350

275

300

325

350

Wavelength (nm)

400

450

500

Wavelength(nm)

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Figure 2 UV-Visible spectra of T. arjuna bark extract, cupric nitrate and Cu2O NPs. Inset shows the formation of Cu2O NPs during the irradiation of reaction mixture.

5000

45 40

625

b- Cu2O 852 1410 895 1645 a

35 30 1384

25

1613

20

b

15

4000

10

3461

0

1000 2000 3000 4000 Wave number in cm-1

ro of

5

3000

(200)

Intensity (cps)

6000

a-MB adsorbed Cu2O

50

% transmitance

7000

55

(110)

(220)

2000 1000

10

20

30

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0 40

50

60

(311)

JCPDS No.85-1326

(111)

8000

70

80

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2 (Cu K radiation)

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Figure 3 Powder XRD pattern of Cu2O NPs (after heating to 700C). Inset shows the FT-IR

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spectra of Cu2O before (b) and after (a) MB adsorption.

60

30

50

25

40

20

qe(mg/g)

35

Dark Light

30

15

20

10

10

5

0

0

200

400

600

800

1000

0

-p

time (min)

ro of

% adsorption

70

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Figure 4 Percentage adsorption (left) and adsorption capacity (right) of MB by Cu2O NPs in dark and light condition [solid : liquid = 10 mg:1.56×10-2 M (100 ml)].

11 10

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9

7 6

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qe(mg/g)

8

5

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4 3

1

2

3

4

5

6

7

8

9

10

11

pH

Figure 5 Effect of pH on MB adsorption capacity by Cu2O NPs.

0.7 Dark Light

0.6 0.5

1/qe

0.4 0.3 0.2 0.1 0.0

0

1

2

3

4

5

6

7

1/Ce

3.6

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Figure 6 Langmuir isotherm of MB on Cu2O NPs in light & dark condition.

Dark Light

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3.0

ln qe

2.4

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1.8 1.2

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0.6

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-1.6

-1.2

-0.8

-0.4

0.0

0.4

0.8

1.2

ln Ce

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Figure 7 Freundlich isotherm of MB on Cu2O NPs in light & dark condition

800

600

400 Dark Light

200

0

0

200

400 600 time(min)

800

1000

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t-q t(min.g/mg)

1000

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Figure 8 Pseudo-second order kinetics model for adsorption of MB on Cu2O NPs in dark and light.

100

% of photodegradation

60 40

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1.2

80

20

0

0.8

0

20

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Absorbance

1.6

40

60

80

100 120

Time (min)

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0.4

0.0 200

300

400

500

600

MB 10 min 30 min 60 min 90 min 120 min

700

800

Wavelenght in nm Figure 9 UV-Vis spectra of MB (1.56×10-2 M) with 0.1g/1000 ml Cu2O NPs in photocatalytic reactor (UV light 250 W) after irradiation to different time and inset shows the % degradation curve.

1.6

ln(C0/Ct)

1.4 1.2 1.0 0.8 0.6 20

40

60

80

100

120

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Time (min)

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Figure 10 Plot of ln (C0/Ct) vs irradiation time for photodegradation of MB by Cu2O NPs.

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Figure 11 Schematic representation of the adsorption and photocatalytic degradation on the surface of Cu2O NPs using MB dye.

ro of -p re lP na ur Jo Figure 12 HPLC chromatograms of MB before and after photocatalytic degradation at  = 246 nm, 292 nm and 668 nm, ([MB] =1.56×10-2 M, catalyst =0.1 g/1000 ml).

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Figure 13 LCMS result of std. MB ([MB] =1.56×10-2 M, catalyst = 0.1 g/1000ml).

Figure 14 LCMS result of photocatalytically degraded MB ([MB] = 1.56×10-2 M, catalyst = 0.1 g/1000ml).

N N

N (H3C)2N

(H3C)2N

S

N(CH3)2

(H3C)2N

S

N(CH3)2

H2N NHCH3 M/Z = 83

HS

N

HS

NH2

(H3C)2N

M/Z = 141

M/Z = 112

NHCH3

M/Z = 268

M/Z = 284

Cl M.W = 319.85

S

S

NH2

M/Z = 241

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Scheme 1. The formation of new products from MB after phtotocatalytic degration by Cu2O NPs under UV irradiation.

Table 1: Langmuir and Freundlich adsorption equilibrium costants of MB on Cu2O NPs.

Model

Parameter qm/(mg.g-1)

KF

KL/(L.mg-1) 0.121 0.108 1/n

R2 0.997 0.999 R2

In Dark

2.3

1.01

0.998

In Light

2.7

1.68

0.999

Langmuir In Dark In Light Freundlich

2.08

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2.53

Table 2: Pseudo second order kinetic model for adsorption of MB on Cu2O NPs. Parameter

Pseudo-second-order kinetic model In Light

qe/(mg.g-1)

k2/(g.mg-1.min-1)

R2

32 .9

6.435 10-3

0.999

In Dark

29 .9

2.3810-4

1

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Model

HPLC signal @

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Table 3. HPLC results of MB before and after phtotocatalytic degradation. Std. MB (5 ppm)

After degradation

Retention time (min) 8.546

36662

246 nm

8.446

1254392

8.467

1149

1928501

8.635

18044

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292 nm

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668 nm

Retention time Area (min) 8.542 4384499

Area