Rate Of Photoreduction Research Articles

Photoreduction of 4-Nitrophenol in the presence of carboxylic acid using CdS nanofibers

The photocatalytic reduction of 4-Nitrophenol was assisted with blue light irradiation using CdS semiconductor nanofiber. The kinetic study of the blue-photoreduction of 4-Nitrophenol to 4-Aminophenol was performed by using Na2SO3 as “hole scavenger” in the presence of middle carboxylic acids (acetic, oxalic and citric acid). The effect of photocatalyst load, the carboxylic acid concentration and of the pH solution (acid, neutral and alkaline media) were investigated. The maximum 4-Nitrophenol photoreduction rate was reached in neutral media and it is related to the enhanced “hole scavenging” effect caused by the SO32− or HSO32− ions in the presence of carboxylic acid. Electrochemical characterization of CdS nanofiber was made in the presence of 4-NP and citric acid. The 4-NP photoreduction reaction follows a zero order reaction and a possible mechanism to explain the fast electron transfer process is discussed as a consequence of the carboxylic acid adsorbed on the CdS surface.

Increasing chloride concentration causes retention of mercury in melted Arctic snow due to changes in photoreduction kinetics

Mercury (Hg) in the Arctic is a significant concern due to its bioaccumulative and neurotoxic properties, and the sensitivity of Arctic environments. Previous research has found high levels of Hg in snowpacks with high chloride (Cl−) concentrations. We hypothesised that Cl− would increase Hg retention by decreasing Hg photoreduction to Hg(0) in melted Arctic snow. To test this, changes in Hg photoreduction kinetics in melted Alert, NU snow were quantified with changing Cl− concentration and UV intensity. Snow was collected and melted in Teflon bottles in May 2014, spiked with 0–10μg/g Cl−, and irradiated with 3.52–5.78W·m−2 UV (280–400nm) radiation in a LuzChem photoreactor. Photoreduction rate constants (k) (0.14–0.59hr−1) had positive linear relationships with [Cl−], while photoreduced Hg amounts (Hg(II)red) had negative linear relationships with [Cl−] (1287–64pg in 200g melted snow). Varying UV and [Cl−] both altered Hg(II)red amounts, with more efficient Hg stabilisation by Cl− at higher UV intensity, while k can be predicted by Cl− concentration and/or UV intensity, depending on experimental parameters. Overall, with future projections for greater snowpack Cl− loading, our experimental results suggest that more Hg could be delivered to Arctic aquatic ecosystems by melted snow (smaller Hg(II)red expected), but the Hg in the melted snow that is photoreduced may do so more quickly (larger k expected).

Cryoprotectants Severely Exacerbate X-ray-Induced Photoreduction.

Approximately 11% of enzymes contain a transition metal ion that is essential for catalytic function. Such metalloenzymes catalyze much of the most chemically challenging and biologically essential chemistry carried out by life. X-ray-based methods, predominantly macromolecular crystallography (MX) and also X-ray absorption spectroscopy (XAS), have proved essential for determining structures of transition metal ion-containing active sites in order to deduce enzyme catalytic mechanisms. However, X-ray irradiation can induce change in both the oxidation state and structure of the metal, which is problematic in structure determination. We present an XAS study of whether cryoprotectants such as polyethylene glycol (PEG) or glycerol, routinely added to MX or XAS samples to improve data quality, affect photoreduction. Our data demonstrate a remarkable 10-fold exacerbation in rate of photoreduction of Cu(II) to Cu(I) when alcohol or ether cryoprotectants are present. Our results suggest that widespread use of cryoprotectants may increase the potential for erroneous structures.

Mercury photoreduction and photooxidation in lakes: Effects of filtration and dissolved organic carbon concentration

Mercury is a globally distributed, environmental contaminant. Quantifying the retention and loss of mercury is integral for predicting mercury-sensitive ecosystems. There is little information on how dissolved organic carbon (DOC) concentrations and particulates affect mercury photoreaction kinetics in freshwater lakes. To address this knowledge gap, samples were collected from ten lakes in Kejimkujik National Park, Nova Scotia (DOC: 2.6–15.4mg/L). Filtered (0.2μm) and unfiltered samples were analysed for gross photoreduction, gross photooxidation, and net reduction rates of mercury using pseudo first-order curves. Unfiltered samples had higher concentrations (p=0.04) of photoreducible divalent mercury (Hg(II)RED) (mean of 754±253pg/L) than filtered samples (mean of 482±206pg/L); however, gross photoreduction and photooxidation rate constants were not significantly different in filtered or unfiltered samples in early summer. DOC was not significantly related to gross photoreduction rate constants in filtered (R2=0.43; p=0.08) and unfiltered (R2=0.02; p=0.71) samples; DOC was also not significantly related to gross photooxidation rate constants in filtered or unfiltered samples. However, DOC was significantly negatively related with Hg(II)RED in unfiltered (R2=0.53; p=0.04), but not in filtered samples (R2=0.04; p=0.60). These trends indicate that DOC is a factor in determining dissolved mercury photoreduction rates and particles partially control available Hg(II)RED in lake water. This research also demonstrates that within these lakes gross photoreduction and photooxidation processes are close to being in balance. Changes to catchment inputs of particulate matter and DOC may alter mercury retention in these lakes and could partially explain observed increases of mercury accumulation in biota.

TiO2@Pt@CeO2 nanocomposite as a bifunctional catalyst for enhancing photo-reduction of Cr (VI) and photo-oxidation of benzyl alcohol

An solar-light-driven and bifunctional photocatalyst was designed for photo-reduction of Cr(VI) and selective photo-oxidation of benzyl alcohol into benzaldehyde in the presence of water under ambient conditions. Double-shelled and sandwiched TiO2@Pt@CeO2 hollow spheres were prepared by using functionalized polystyrene spheres, sol-gel, hydrothermal reaction, and calcination. The Pt nanoparticles (NPs) were controllably loaded between the TiO2 shell and CeO2 shell. Under solar-light irradiation, the photo-reduction rate of Cr(VI) (μmol h−1) was in the order of TiO2@Pt@CeO2 (1.901) > TiO2@CeO2 (1.424) > TiO2 (1.040) > CeO2 (0.992). Among the above-mentioned photocatalysts, the conversion rate of benzyl alcohol for TiO2@Pt@CeO2 was also the best. These results were attributed to the combination of TiO2 and CeO2 as photocatalyst and oxygen buffer, the double-shelled and sandwiched nanostructure, and the addition of Pt NPs as cocatalyst and electron trap site, which could store and shuttle photo-generated electrons, reduce the recombination of the electron-hole, and then enhance photo-generation of active radicals. This conclusion was verified by the electron paramagnetic resonance (EPR) spectroscopy. Considering the versatile combination of photocatalyst, oxygen buffer and cocatalyst, this work could provide new insights into the design of high-performance bifunctional photocatalysts for heavy metal removal and selective synthesis.

Photodeposition of Pd nanoparticles on TiO2 using sacrificial organic alcohols

Samples of deposited Pd on titania were prepared through photoreduction method in the absence and presence of different organic alcohols with different carbon numbers and molar weights as sacrificial electron donors (SED). It was observed that palladium nanoparticles were photoreduced and deposited with the rates of 0.55, 0.54, 0.44, and 0.38 μmol/g/min on titania in the presence of methanol, ethanol, ethylene glycol, and 1-propanol, respectively. However, the deposition rate was 0.22 μmol/g/min in the absence of any SED, indicating the significant enhancement of reduction rate in the presence of the alcohols. The results proved that the alcohols with lower carbon numbers and molar weights resulted in a higher reduction rate of Pd on TiO2. The highest rate of Pd photoreduction (0.55 μmol/g/min) was obtained by using methanol, in which the highest dispersion percentage of metal palladium particles (22.32%) with the highest depositing amount (2.8 wt%) was measured. In addition to the FT-IR spectra of the surface palladium carbonyls, atomic absorbance spectroscopy and pulse CO chemisorption evaluations showed that employing a higher reduction rate is a key factor in obtaining a high palladium loading on TiO2. XRD patterns showed that all the Pd particles were deposited in metallic form. According to the EDS analysis, ethylene glycol was the most appropriate SED in complete removal of Cl.

Metal-promoted titania photocatalysis for destruction of nitrates and organics from aqueous environments.

This review article provides an overview of activities in the rapidly developing field of water purification via photocatalytic methods and focuses on the removal of nitrate ions with simultaneous removal of the hole scavenger. Many of the issues associated with provision of potable water in the developing world may be resolved by the use of simple physical methodologies such as filtration. However, many of the issues associated with water purity in the developed world involve complex, stable molecules present at low concentrations that are nonetheless capable of producing toxic effects in plants and animals and that require more demanding removal technologies. Photocatalytic methods can be operated remotely and often show minimal production of undesired side products. Titania alone shows limitations, not only in terms of the slow rate of photoreduction of nitrate but also in terms of selectivity and the need to employ radiation in the UV region due to the magnitude of the band gap. Key challenges may be defined as: reducing the band gap/increasing absorption in the visible region, enhancing the adsorption capacity/access to the surface sites and reducing the rate of hole/electron recombination. The present article will focus on the use of titania-based materials that involve metal co-catalysts for nitrate reduction.This article is part of a discussion meeting issue 'Providing sustainable catalytic solutions for a rapidly changing world'.

Self-propagation combustion method for the synthesis of solar active Nano Ferrite for Cr(VI) reduction in aqua system

Abstract The study aimed at the development of a facile route to the synthesis of a solar active nano ferrite via the self-propagation combustion protocol. The solar activity of the synthesised ferrite sample (FSP) was determined using the reduction of Cr(VI) to Cr(III) as a case study, in the presence of oxalic acid, as the hole scavenger. The analysis of the time-concentration profile data of the photoreduction reaction with the pseudo first order kinetic equation showed that the rate and half-life (t1/2) of photoreduction of Cr(VI) to Cr(III) is dependent on the initial Cr(VI) concentration. The photoreduction efficiency (PE) (%) of the FSP is a function of the initial FSP dosage and the hole scavenger. The determination of the influence of hydrochemistry on the PE (%) showed that Cr(VI) solution pH and ionic strength had no visible negative impact. Aside the presence of carbonate in the Cr(VI) solution, other anionic interfering species (i.e. NO−3, Cl− and SO3 2−) had minimal or no visible influence on the PE (%) values. The presence of carbonate, at higher concentration (i.e. ˃10 mg/L) significantly impacted on the PE values and hyperchromic shift in the absorbance values of the treated water from the photo reduction process was observed. The tendency of the Cr(III) that is formed from the photoreduction reaction to form Cr(III)-oxalato complex was confirmed after a certain minimum time of the photoreduction process.

CO2 photoreduction on hydroxyl-group-rich mesoporous single crystal TiO2

Mesoporous TiO2 single crystal coated with O vacancies, Ti3+ and OH groups was synthesized by a simple hydrothermal method. Mesoporous form as the growth of TiO2. O vacancies and Ti3+ form with different origins. According to sample’s morphology, specific surface areas, CO2 adsorption capacity and photocatalytic activity, OH groups can improve the reaction rate of CO2 photoreduction, and O vacancies and Ti3+ can influence the utilization of phtogenerated carriers. The photocatalytic activity reaches an optimal value with the calcination condition change, which adjusts the amount of these chemical composition: OH groups, O vacancies and Ti3+.

Revisiting Mn and Fe removal in humic rich estuaries

Metal removal by estuarine mixing has been studied for several decades, but few studies emphasize dissolved metal speciation and organic ligand complexation. Findings from the last decade indicate that metal-humic complexation can be significant for dissolved metals including Cu(II), Al(III) and Fe(III), but little consideration is given to the precipitation of these complexes with humic material at pH<2. Given that total soluble metal analysis involves an acidification step for sample preservation, we show that Mn and other metal concentrations may have been underestimated in estuaries, especially when humic substance concentrations are high. A competitive ligand assay of selected samples from our study site, a coastal waterway bordered by wetlands (Broadkill River, DE), showed that Mn(III)-humic complexation is significant, and that some Mn(III)-L complexes precipitate during acidification. In the oxygenated surface waters of the Broadkill River, total dissolved Mn (dMnT) was up to 100% complexed to ambient ligands as Mn(III)-L, and we present evidence for humic-type Mn(III)-L complexes. The Mn(III) complexes were kinetically stabilized against Fe(II) reduction, even when [Fe(II)] was 17 times higher than [dMnT]. Unlike typical oceanic surface waters, [Fe(II)]>[Fe(III)-L] in surface waters, which may be attributed to high rates of photoreduction of Fe(III)-L complexes. Total [Mn(III)-L] ranged from 0.22 to 8.4μM, in excess of solid MnOx (below 0.28μM in all samples). Filtration of samples through 0.02μm filters indicated that all Mn(III)-L complexes pass through the filters and were not colloidal species in contrast to dissolved Fe. Incubation experiments indicated that the reductive dissolution of solid MnOx by ambient ligands may be responsible for Mn(III) formation in this system. Unlike previous studies of estuarine mixing, which demonstrated metal removal during mixing, we show significant export of dMn and dissolved Fe (dFe) in the summer and fall of 2015. Thus, we propose that estuarine removal should be considered seasonal for dMn and dFe, with export in the summer and fall and removal during the winter.

Photoluminescence-based real-time monitoring of graphene oxide photoreduction: Demonstrations and application to graphene oxide/titanium dioxide composites

Reduction of graphene oxide (GO) is a key process toward simple and massively scalable production of graphene. Analytic techniques such as X-Ray diffraction, X-Ray photoemission spectroscopy and Raman spectroscopy are excellent for ex-situ post-process assessment of the state of reduction of GO, but are unsuited for a real-time analysis during the process itself. In this work, we show that photoluminescence (PL) spectroscopy can be effectively used to this aim, allowing tracing the time dynamics of photoreduction processes. A proof-of-concept is shown, using a low-cost setup, by considering the case of pristine GO samples and of GO/titanium dioxide (TiO2) composites. We show that the PL analysis allows evidencing in real time the TiO2-induced photocatalytic contribution to GO photoreduction and the changes in photoreduction rates caused by the presence of oxygen and water molecules adsorbed on GO surfaces.

Influence of TiO2 hollow sphere size on its photo-reduction activity for toxic Cr(VI) removal

After polystyrene@titanium dioxide (PS@TiO2) composite with different size was calcined at designated temperature, TiO2 hollow sphere with controllable size was obtained for high efficient photo-reduction of Cr(VI). The feature of the TiO2 hollow sphere was investigated by SEM, TEM, XRD, UV–Vis, and photoluminescence. The photo-reduction of Cr(VI) were measured for the performance assessment of the TiO2 hollow sphere, Cr(VI) was used as an electron acceptor. After irradiation for 2h, the photo-reduction rate of Cr(VI) (pH=2.82) for TiO2(450nm) was 96%, which exhibited an increase of 5% and 8% compared with TiO2(370nm) and TiO2(600nm). The absorption edges of TiO2 hollow sphere (450nm) was largest with the increasing of hollow sphere size from 370 to 600nm. The optimal hollow sphere size of TiO2 was 450nm for the photo-reduction of Cr(VI), because the light-harvesting efficiency (the best of absorption edge) and photo-generated electron-hole separation rate (the best of photo-reduction rate) of TiO2 hollow sphere were controlled by its hollow sphere size. In addition, we find that the behavior of the hydrogen production was inhibited by the coexistence Cr(VI) solution. This study can improve our understanding of the mechanism for the activity enhancement by the optimal hollow sphere size of TiO2.

Visible-solar-light-driven photo-reduction and removal of cadmium ion with Eosin Y-sensitized TiO2 in aqueous solution of triethanolamine

Abstract Cadmium is toxic to humans, animals, and plants, and show persistence because of its non-degradability. Photo-reduction of cadmium ion (Cd (II)) was studied with Eosin Y-sensitized TiO2 photocatalyst for the reduction/removal of Cd (II) in an aqueous medium under visible-solar light. Triethanolamine (TEOA) was used as a sacrificial electron donor. The band-gap of Eosin Y-sensitized TiO2 photocatalyst was reduced by ∼1 eV, and visible light activity was observed for Cd (II) photo-reduction. Parametric studies were performed for visible-solar light intensity, solution pH, and initial concentrations of metal ion, dye, photocatalyst, and an electron donor. Complete photo-reduction of Cd (II) was achieved in 3 h at a pH of 7.0 and a light intensity of 100 mW cm−2. The photo-reduction rate of Cd (II) in TEOA solution followed Langmuir-Hinshelwood rate equation. The highest apparent quantum yield (∼0.3%) for Cd (II) photo-reduction was observed at the lower visible light intensity with illuminated Eosin Y-sensitized TiO2.

High rates of Cr(VI) photoreduction with magnetically recoverable nano-Fe 3 O 4 @Fe 2 O 3 /Al 2 O 3 catalyst under visible light

Abstract Core-shell type Fe 3 O 4 @Fe 2 O 3 was dispersed over nano Al 2 O 3 support using aqueous medium co-precipitation method. The Fe 3 O 4 core offers magnetic recoverability, while the shell Fe 2 O 3 , due to its optimal band gap, provides photocatalytic activity in the visible light region. The concentration of Fe 3 O 4 @Fe 2 O 3 was varied and the synthesized materials were characterized using XRD, TEM, XPS, Raman spectroscopy, diffuse reflectance spectroscopy and BET surface area measurement. The synthesized materials were studied for Cr(VI) visible light photoreduction. Oxalic acid was used as a hole scavenger and Cr(VI) was efficiently reduced under visible light in aerobic condition. Even with 5% Fe 3 O 4 @Fe 2 O 3 /Al 2 O 3 the rate of photoreduction was orders of magnitude higher than that of bulk Fe 3 O 4 @Fe 2 O 3 . The obtained rates with the synthesized catalysts were compared with the literature and were found to be superior to the reported catalysts. The 40% Fe 3 O 4 @Fe 2 O 3 /Al 2 O 3 catalyst showed magnetic recoverability and the catalytic efficiency was stable up to 4 cycles.

Changes in active site histidine hydrogen bonding trigger cryptochrome activation

Cryptochrome (CRY) is the principal light sensor of the insect circadian clock. Photoreduction of the Drosophila CRY (dCRY) flavin cofactor to the anionic semiquinone (ASQ) restructures a C-terminal tail helix (CTT) that otherwise inhibits interactions with targets that include the clock protein Timeless (TIM). All-atom molecular dynamics (MD) simulations indicate that flavin reduction destabilizes the CTT, which undergoes large-scale conformational changes (the CTT release) on short (25 ns) timescales. The CTT release correlates with the conformation and protonation state of conserved His378, which resides between the CTT and the flavin cofactor. Poisson-Boltzmann calculations indicate that flavin reduction substantially increases the His378 pKa Consistent with coupling between ASQ formation and His378 protonation, dCRY displays reduced photoreduction rates with increasing pH; however, His378Asn/Arg variants show no such pH dependence. Replica-exchange MD simulations also support CTT release mediated by changes in His378 hydrogen bonding and verify other responsive regions of the protein previously identified by proteolytic sensitivity assays. His378 dCRY variants show varying abilities to light-activate TIM and undergo self-degradation in cellular assays. Surprisingly, His378Arg/Lys variants do not degrade in light despite maintaining reactivity toward TIM, thereby implicating different conformational responses in these two functions. Thus, the dCRY photosensory mechanism involves flavin photoreduction coupled to protonation of His378, whose perturbed hydrogen-bonding pattern alters the CTT and surrounding regions.

Photocatalytic reduction of 4-nitrophenol on in situ fluorinated sol–gel TiO2 under UV irradiation using Na2SO3 as reducing agent

The in situ fluorination of the TiO2 semiconductor was performed via sol–gel method. Photocatalysts with different fluoride percentage were synthesized using ammonium fluoride as hydrolysis catalyst and as anionic precursor. For comparison, sol–gel TiO2 was also studied as a reference material. The solids were characterized using several techniques in order to analyze their structural, textural and optical properties. The fluorination of the TiO2 favored the preferential formation of the anatase phase and an increase in the crystallinity; in contrast, a decrease in the specific surface area was observed. The photocatalytic activity of the materials was evaluated in the 4-nitrophenol photoreduction to 4-aminophenol using Na2SO3 as reducing agent under UV light irradiation. It was found that the generation of the ≡Ti–F surface species increased the photocatalytic properties of the semiconductor; thus, the 4-nitrophenol photoreduction rate using the fluorinated solids was higher compared with the sol–gel TiO2 and Degussa P-25. Favorable efficiency in the photoreduction of the 4-NP molecule after the recycling experiments of the photocatalyst was observed.

Controlling Au Photodeposition on Large ZnO Nanoparticles.

This study investigated how to control the rate of photoreduction of metastable AuCl2(-) at the solid-solution interface of large ZnO nanoparticles (NPs) (50-100 nm size). Band-gap photoexcitation of electronic charge in ZnO by 370 nm UV light yielded Au NP deposition and the formation of ZnO-Au NP hybrids. Au NP growth was observed to be nonepitaxial, and the patterns of Au photodeposition onto ZnO NPs observed by high-resolution transmission electron microscopy were consistent with reduction of AuCl2(-) at ZnO facet edges and corner sites. Au NP photodeposition was effective in the presence of labile oleylamine ligands attached to the ZnO surface; however, when a strong-binding dodecanethiol ligand coated the surface, photodeposition was quenched. Rates of interfacial electron transfer at the ZnO-solution interface were adjusted by changing the solvent, and these rates were observed to strongly depend on the solvent's permittivity (ε) and viscosity. From measurements of electron transfer from ZnO to the organic dye toluidine blue at the ZnO-solution interface, it was confirmed that low ε solvent mixtures (ε ≈ 9.5) possessed markedly higher rates of photocatalytic interfacial electron transfer (∼3.2 × 10(4) electrons·particle(-1)·s(-1)) compared to solvent mixtures with high ε (ε = 29.9, ∼1.9 × 10(4) electrons·particle(-1)·s(-1)). Dissolved oxygen content in the solvent and the exposure time of ZnO to band-gap, near-UV photoexcitation were also identified as factors that strongly affected Au photodeposition behavior. Production of Au clusters was favored under conditions that caused electron accumulation in the ZnO-Au NP hybrid. Under conditions where electron discharge was rapid (such as in low ε solvents), AuCl2(-) precursor ions photoreduced at ZnO surfaces in less than 5 s, leading to deposition of several small, isolated ∼6 nm Au NP on the ZnO host instead.

Effect of solvent nature on the photoreduction kinetics of substituted benzoquinones

Effect of the solvent nature on the kinetics of photoreduction of substituted benzoquinones in the presence of hydrogen donors has been studied. It has been found that the effective photoreduction rate constant (kH) for quinones decreases with an increase in solvent polarity. For the 3,6-di-tert-butylbenzoquinone–1,2-N,N-dimethylaniline pair, the dependence of ln kH on the difference of the reciprocals of optical and static solvent permitivities (1/e ∞–1/e0) is stepwise with a break point corresponding to CH2Cl2. A similar relationship lnkH = f(1/e ∞–1/e0) is observed for the p-chloranil–mesitylene pair. In the study of the photoreduction kinetics for a series of seven o-benzoquinones in the presence of p-derivatives of N,N-dimethylaniline in CH2Cl2, it has been found that the dependence of kH on the free energy of electron transfer (ΔGe) has a maximum for the 3,6-di-tert-butylquinone-1,2–N,N-dimethylaniline pair at ΔGe = 0.11 eV.

An ecological new approach for treating Cr(VI)-containing industrial wastewater: Photochemical reduction

An ecological new approach for photochemical reduction of Cr(VI) in aqueous solution by adding into water-soluble copolymer, polyethylene glycol (PEG), was investigated. Various influences including light intensity, initial solution pH value, PEG molecular weight and initial concentration ratio of PEG to Cr(VI) on photochemical reduction of Cr(VI) were discussed, and a possible reaction mechanism was proposed. Experimental results revealed that Cr(VI) could be reduced to Cr(III) by PEG under sunlight irradiation. The photo-reduction rate of Cr(VI) increased with the decrease of solution pH and PEG molecular weight, but increased with the light intensity. The reduction percentage of Cr(VI) increased with the initial concentration ratio of PEG to Cr(VI). When the initial solution pH value was below 3.0, almost all of Cr(VI) was completely reduced to Cr(III) within 20 min of 50 × 103 lux solar irradiation in the presence of PEG. After photo-reduction, PEG and Cr(III) in aqueous solutions could be recovered by adding into a high-concentrated Na2SO4 aqueous solution to induce the formation of a stable PEG-based aqueous biphasic system. By doing so, Na2SO4 in aqueous solution could also be removed. The present work highlights a promising new route for treating the industrial wastewater containing toxic Cr(VI) ions by adding into environmental-friendly PEG for photo-reduction of Cr(VI) to Cr(III), and then salting-out recovery of PEG and removal of Cr(III) in wastewater by adding into another high-salt wastewater, so that the high-salt wastewater could also be treated.

Acrylate-based Polymerizable Sol–Gel Synthesis of Magnetically Recoverable TiO2 Supported Fe3O4 for Cr(VI) Photoreduction in Aerobic Atmosphere

TiO2 synthesized by polymerizable sol–gel approach is used to demonstrate the photoreduction of Cr(VI) in aqueous medium. Fe3O4 is chosen as the magnetically recoverable support, onto which, 10, 20, 30 and 50% of TiO2 have been dispersed following the polymerizable sol–gel approach. The synthesized materials are characterized using XRD, SEM, XPS, Raman spectroscopy, diffuse reflectance spectroscopy and BET surface area measurement. Different hole-scavengers (oxalic acid, ammonium oxalate and ethanol) and an electron scavenger (potassium periodate) have been studied to compare the efficiency of Cr(VI) photoreduction in nitrogen as well as air atmosphere. With 5 mM oxalic acid as the hole-scavenger, the TiO2/Fe3O4 materials have demonstrated superior activity to the nonsupported bulk TiO2 toward Cr(VI) photoreduction in aerobic atmosphere. Particularly, 30% TiO2/Fe3O4 has shown the highest Cr(VI) photoreduction rate among the lot. The 30% TiO2/Fe3O4 catalyst has also demonstrated good recoverability as well...