Photocatalytic Reduction Of Nitrate Research Articles

Photocatalytic denitrification of water using polystyrene immobilized TiO2 as floating catalyst

The current work demonstrates the feasibility of polystyrene (PS) immobilized TiO2 (PS-TiO2) as a floating catalyst for the photocatalytic reduction of nitrate in aqueous solution with formic acid as a hole scavenger. The synthesized PS-TiO2 was characterized by X-ray diffraction (XRD), scanning electron micrograph (SEM), Fourier transform infrared spectroscopy (FT-IR), and the Brunauer–Emmett–Teller (BET) surface area analysis. The experimental conditions including initial pH of the solution, formic acid concentration, and catalyst dosage were varied to demonstrate their effect on the denitrification efficiency and nitrogen selectivity. The complete denitrification of water with 40 mg L-1 nitrate (as N) was observed within 135 min of irradiation at initial pH of 2.5, catalyst dosage of 15 g L-1, and 16 mM formic acid concentration. The floating nature of the catalysts allowed for their easy recovery with ≥ 98 % catalyst recovery after 5 cycles of denitrification experiments. A potential mechanism for photocatalytic denitrification in the process is also discussed.

Nitrate photocatalytic reduction on TiO2: Metal loaded, synthesis and anions effect

Herein we report the study of the photocatalytic reduction of nitrate by TiO2 in presence of inorganic anions and for TiO2 loaded with Ag+, Cu2+, Ni2+, and Fe3+ by following the wet impregnation method. All photocatalytic assays were performed in solution containing formic acid as scavenger of the photogenerated holes (hvb+). The observed dependence of the photocatalytic nitrate reduction on the concentration of HCOOH suggests this specie is oxidized at hvb+ forming CO2− radicals that, in turn, reduces NO3− to N2. The photocatalytic assays in presence of H2PO4−, SO42−, HCO3−, F− and Cl− indicated the surface anionization leading to hvb+ blocking and, as consequence, to the decrease of HCOOH oxidation. Indeed, impedimetric data indicated the adsorbed anions on TiO2 are mainly responsible for hindering the interaction between the electron donor (HCOOH) and the photocatalyst. Among the metal ions used for loading, only Ag+ was efficient in storage the photogenerated electrons (ecb−) with a performance improvement of 15.5 % in respect to the neat TiO2 catalyst. Experiments carried out with groundwater samples showed an activity loss that was assigned to the catalyst poisoning by other ions, although with selectivity to N2 close to 100 %.

Novel direct dual Z-scheme AgBr(Ag)/MIL-101(Cr)/CuFe2O4 for efficient conversion of nitrate to nitrogen

Photocatalytic reduction of nitrate has attracted much attention recently, however, low efficiency and difficult separation have limited its application in practice. In this study, the novel direct dual Z-scheme AgBr(Ag)/MIL-101(Cr)/CuFe2O4 (AB/M/CFO) was fabricated by the hydrothermal technology combined with the photodeposition method for the first time. The AB/M/CFO exhibited the highest nitrate conversion and nitrogen selectivity (79.9% and 94.5%, respectively) compared to AgBr(Ag)/MIL-101(Cr), MIL-101(Cr) and CuFe2O4 for 30 min UV-light irradiation. The dual Z-scheme of AB/M/CFO enhanced electron transfer and charge separation, which was proved by transient photocurrent responses, leading to a significant improvement in photocatalytic efficiency. Meanwhile, after four cycles, the AB/M/CFO photocatalyst also displayed a strong magnetic separation ability and excellent recycling stability. Furthermore, the excitation and electron transfer process over dual Z-scheme AB/M/CFO photocatalytic material were proposed, based on the radical trapping experiments. Our work provides a new strategy to construct dual Z-scheme MOFs-based materials that have promising applications in photocatalytic reduction of pollutants.

Fabrication of novel 2D Ag-TiO2/γ-Al2O3/Chitosan nano-composite photocatalyst toward enhanced photocatalytic reduction of nitrate

The presence of excess nitrate in groundwater limits it use as a drinking water supply and its removal is critical to balance the nitrogen cycle in aquatic systems. In this study, ultra-thin 2-dimensional Ag-TiO2/γ-Al2O3/Chitosan (Ag-TiO2/Al2O3/CS) nano-composite was synthesized for the fast reduction of nitrate under UVA irradiation from aqueous solutions. As-synthesized nano-composite was well characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption-desorption isotherms, Fourier-transform infrared spectroscopy and UV–vis diffuse reflectance spectroscopy. Experimental variables including pH, nitrate concentration, photocatalyst dose and contact time were considered to demonstrate their effect on the rate of nitrate reduction. Formic acid was used as a radical scavenger at optimal concentration of 2:1 (formic acid:nitrate). The results showed that upon UVA irradiation, the synthesized nano-composite exhibited fast nitrate reduction in broad pH range (about 74% removal at pH 11 in 5 min reaction time) in diverse water chemical conditions. The Ag-doped and hybrid heterostructures can effectively utilize UV–visible-light to remove nitrate and degrade formic acid. For the 3 cycles the photocatalyst efficiency remained same and after the third cycle, its efficacy decreased gradually. This work suggests 2D Ag-TiO2/Al2O3/CS nano-composite for the fast removal of nitrate in drinking water treatment.

A Mechanism Investigation of how the Alloying Effect Improves the Photocatalytic Nitrate Reduction Activity of Bismuth Oxyhalide Nanosheets

AbstractAlloyed bismuth oxyhalides have been widely used in photocatalytic water treatment processes due to their superior photocatalytic activity. However, there is no report on the removal of NO3− for alloyed bismuth oxyhalides, and the mechanism of the effect of alloying on NO3− reduction activity is still unclear. In this work, we prepared a series of BiOClnBr1‐n (0≤n≤1) with different Cl/Br ratios but with controlled similar morphologies, and explored their catalytic activities on reducing NO3− under visible light irradiation. Density functional theory investigations revealed that the formation energy for an oxygen (O) vacancy on the surface of BiOClnBr1‐n alloys is clearly reduced in comparison with the monohalide, illustrating that more O vacancies can be produced on the surface of BiOClnBr1‐n alloys. A high concentration of O vacancies not only promotes the adsorption of NO3− but also enhances the separation efficiency of the photogenerated electron‐hole (e–h) pairs, with both being beneficial to enhance the photocatalytic activity of BiOClnBr1‐n alloys for NO3− reduction. These new discoveries not only promote the design and development of new photocatalysts with excellent NO3− reduction properties, but also help to understand the relationship between alloying effects and semiconductor photocatalytic properties.

Novel Z-Scheme Ag/TiO2/AgMIL-101(Cr) as an efficient photocatalyst for nitrogen production from nitrate

Z-Scheme Ag/TiO2/AgMIL-101(Cr) was prepared by co-doping Ag and TiO2 with AgMIL-101(Cr) via solvothermal synthesis combined with sol-gel method. Ag and anatase TiO2 nanoparticles were well dispersed on the surface of AgMIL-101(Cr) with octahedral structure. 5 wt% Ag and 50% TiO2 co-doping on the AgMIL-101(Cr) (Ag5T50Ag5M) exhibited large specific surface area (346.5 m2·g−1) and narrow band gap 2.16 eV. Only 10 min of UV light irradiation resulted in the conversion of nitrate and nitrogen selectivity up to 100% over Ag5T50Ag5M. After 5 cycles of nitrate removal, the conversion of nitrate remained 90% indicating that catalyst had stable reusability. Moreover, instead of formic acid, ofloxacin (OFX) was used as a hole scavenger to evaluate the ability of Ag5T50Ag5M for the nitrate reduction. The result showed that the concentration of OFX was important factor to affect the conversion of nitrate. Based on the above discussion about the characterization and photocatalytic nitrate reduction, combined with the photoluminescence and electrochemical measurement results, the enhanced conversion of nitrate and nitrogen selectivity was reasonably explained. Finally, the route of electron transfer during the three constituents constructed Z-Scheme system and the mechanism of nitrate reduction to nitrogen was presumed.

Microwave synthesised Pd–TiO2 for photocatalytic ammonia production

Palladium doped anatase TiO2 nanoparticles were synthesised by a rapid (3 min) one-pot microwave synthesis technique at low temperature and pressure. After being fully characterised by SEM, XRD, Raman, XPS and EDX, photocatalytic nitrate reduction and ammonia production were studied over various dopant levels between 0–3.97 wt% Pd and compared to similar previous literature. Improved yields of ammonia were observed with most dopant levels when compared to non-doped microwave synthesised TiO2 with 2.65 wt% found to be the optimum dopant level producing 21.2 μmol NH3. Electrochemical impedance spectroscopy of TiO2 and Pd–TiO2 photoelectrodes revealed improvements in charge transfer characteristics at high Pd dopant levels.

Catalytic and Photocatalytic Nitrate Reduction Over Pd-Cu Loaded Over Hybrid Materials of Multi-Walled Carbon Nanotubes and TiO2.

TiO2 and carbon nanotube-TiO2 hybrid materials synthesized by sol-gel and loaded with 1%Pd−1%Cu (%wt.) were tested in the catalytic and photocatalytic reduction of nitrate in water in the presence of CO2 (buffer) and H2 (reducing agent). Characterization of the catalysts was performed by UV-Vis and fluorescence spectroscopy, X-ray diffraction, temperature programed reduction, N2 adsorption, and electron microscopy. The presence of light produced a positive effect in the kinetics of nitrate removal. Higher selectivity toward nitrogen formation was observed under dark condition, while the photo-activated reactions showed higher selectivity for the production of ammonium. The hybrid catalyst containing 20 %wt. of carbon nanotubes shows the best compromise between activity and selectivity. A mechanism for the photocatalytic abatement of nitrate in water in the presence of the hybrid materials was proposed, based in the action of carbon nanotubes as light harvesters, dispersing media for TiO2 particles and as charge carrier facilitators.

Improving Photocatalytic Water Treatment through Nanocrystal Engineering: Mesoporous Nanosheet-Assembled 3D BiOCl Hierarchical Nanostructures That Induce Unprecedented Large Vacancies.

Vacancy control can significantly enhance the performance of photocatalytic semiconductors for water purification. However, little is known about the mechanisms and approaches that could generate stable large vacancies. Here, we report a new mechanism to induce vacancy formation on nanocrystals for enhanced photocatalytic activity: the introduction of mesopores. We synthesized two nanosheet-assembled hierarchical 3D BiOCl mesoporous nanostructures with similar morphology and exposed facets but different nanosheet thickness. Positron annihilation analysis detected unprecedentedly large VBi‴ VO•• VBi‴ VO•• VBi‴ vacancy associates (as well as VBi‴ VO•• VBi‴) on BiOCl assembled from 3-6 nm nanosheets but only VBi‴ VO•• VBi‴ vacancy associates on BiOCl assembled from thicker (10-20 nm) nanosheets. Comparison of vacancy properties with 2D ultrathin 2.7 nm nanosheets (with VBi‴ VO•• VBi‴ and VBi‴) indicates that nanosheet thinness alone cannot explain the formation of such large atom vacancies. On the basis of density functional theory computations of formation energy of isolated Bi vacancy, we show that mesopores facilitate the formation of large vacancies to counterbalance thermodynamic instability caused by incompletely coordinated Bi and O atoms along the mesopore perimeters. We corroborate that the extraordinarily large VBi‴ VO•• VBi‴ VO•• VBi‴ vacancy associates facilitate photoexcitation of electrons and prevent the recombination of electron-hole pairs, which significantly enhances photocatalytic activity. This is demonstrated by the rapid mineralization of bisphenol A (10-5 M) with low photocatalyst loading (1 g L-1), as well as enhanced bacterial disinfection. Improved electron-hole separation is also corroborated by enhanced photocatalytic reduction of nitrate.

PdSn/NiO/NaTaO3:La for photocatalytic ammonia synthesis by reduction of NO3− with formic acid in aqueous solution

Photocatalytic ammonia synthesis is of great importance but remains very challenging in photocatalysis. Here, we fabricated a photocatalytic reaction system for the efficiently photocatalytic nitrate reduction to ammonia under UV irradiation using PdSn/NiO/NaTaO3:La as a photocatalyst in the presence of formic acid. Several important factors of the photocatalytic performance were investigated, including initial concentration of the nitrate solution, initial pH value and cocatalyst loadings. Nitrate conversion reaches 100% and ammonia selectivity is 72% over the optimum photocatalyst with 5% bimetallic PdSn alloy and 0.2% NiO loadings. The outstanding performance of photocatalyst can be ascribed to both the strong adsorption of nitrite on NiO and the efficient separation of electron-hole pairs by PdSn bimetallic alloy. Besides as the hole scavenger, formic acid also provides not only carboxyl anion radicals for nitrate reduction but also the in-situ buffer effect on ammonia formation. These results give inspiration for designing the reactive system with efficient photocatalytic ammonia synthesis.

Novel Pd/GdCrO3 composite for photo-catalytic reduction of nitrate to N2 with high selectivity and activity

Although photocatalytic reduction of nitrate attracted much attention recently, undesired intermediate products (nitrite and ammonium) limited its application in practice. In this study, novel Pd/GdCrO3 composite was successfully synthesized to photo-catalytically reduce nitrate to N2 with high selectivity. Compared with TiO2 (P25), GdCrO3, Ag/GdCrO3 and Cu/GdCrO3, 1 wt% Pd/GdCrO3 achieved higher removal rate of nitrate (98.7%) and selectivity to N2 (100%). The kinetics constant of 1 wt% Pd/GdCrO3 was two times higher than that of P25. Even after six cycling runs, 1 wt% Pd/GdCrO3 still remained high photocatalytic reduction rate of nitrate (95.5%) and selectivity to N2 (98.4%). Such advantages were not only attributed to the negative conduction band value of GdCrO3 but also attributed to the co-catalyst effect of Pd. On one hand, nano particles Pd improved the utilization of charge carriers of GdCrO3. On the other hand, nitrite was easily reduced to NO* on nano particles Pd surface, followed by decomposition step to N* and O*, and then the reduction of nitrite in the vicinity of the N* could yield N2O* which would be preferentially transformed into N2. Accordingly, high concentration of nitrite accumulated initially could enhance the likelihood of N* encountering nitrite so as to increasing the N2 selectivity. In addition, electron paramagnetic resonance and hole scavenger experiments demonstrated that both photo-generated electrons and CO2− played important role in photocatalytic reduction process, suggesting a different mechanism from P25 where nitrate was mainly reduced by CO2−. Thus, the present work not only prepared a promising photocatalyst for reduction of nitrate in water/wastewater treatment process, but also provided a simple and efficient way to improve the photocatalytic activity and selectivity to N2of photocatalysts.

All that Glitters Is Not Gold: A Probe into Photocatalytic Nitrate Reduction Mechanism over Noble Metal Doped and Undoped TiO2

Photocatalytic reduction of aqueous nitrate has been thoroughly studied over noble metals doped and pristine TiO2 synthesized by a customized single step microwave assisted hydrothermal method. The synthesized catalysts are systematically characterized using XRD, Raman spectroscopy, FE-SEM, HR-TEM, XPS, diffuse reflectance spectroscopy, and PL measurements. The characterization reveals the successful synthesis of highly crystalline doped and undoped nano-TiO2. The photocatalytic rate of aqueous nitrate reduction over undoped TiO2 is found to be higher than that of noble metal doped TiO2. Mechanistic studies of the photocatalytic reduction are carried out with the help of different hole (oxalic acid, and methanol) and electron (sodium persulfate) scavengers, which reveal that the photogenerated electrons are the primary agents toward efficient nitrate photoreduction. Detailed studies have revealed that the noble metal doping in TiO2 helps in efficient photogeneration of H2 compared to the undoped analogue,...

Influence of ultraviolet wavelengths on kinetics and selectivity for N-gases during TiO2 photocatalytic reduction of nitrate

For drinking water applications, photocatalytic reduction processes beneficially transform aqueous nitrate to innocuous nitrogen gases (N-gases) but can produce nitrite and ammonia as undesirable aqueous by-products. We hypothesize that by-product selectivity is a function of light source and photon fluence dose, such that discrete wavelengths can increase yield of desirable N-gases. Experiments performed under different wavelength irradiation (ultraviolet- [UV] A, B, C) reduced nitrate in water to differing extents based on pH over the range of 1–8 or the presence of soluble organic electron donors. At an equivalent photon fluence dose, the most rapid nitrate loss in acidic solutions occurred using a combination of three UV-light emitting diodes (285nm, 300nm, 365nm) closely followed by a polychromatic medium pressure UV lamp. A polychromatic xenon light source was least effective in reducing nitrate. Nitrite is an important intermediate during photocatalytic reduction of nitrate. Nitrite absorbs 330–380nm light with high quantum efficiency. Thus, polychromatic or monochromatic light sources with strong UV-A emission more rapidly convert nitrite to by-products than UV-C monochromatic light sources. Nitrous acid (HONO) has a higher molar absorptivity (ε) and quantum efficiency than nitrite ion (pKa=3.39) around 350–370nm. Selectivity towards N-gases is bifurcated at the nitrite intermediate and is strongly influenced by direct photolysis instead of photocatalytic reduction. Thus, the selectivity of by-products can be controlled by delivering light in the 350–370nm wavelength range, where it enables photocatalytic processes to rapidly initiate NO3− reduction and delivers photons for direct photolysis of HONO.

Simultaneous photocatalytic removal of nitrate and oxalic acid over Cu2O/TiO2 and Cu2O/TiO2-AC composites

Cu2O/TiO2 (1–10wt% Cu2O) and 2.5% Cu2O/TiO2-AC (2.5–20wt% AC) photocatalyst composites were synthesised by an ethanol reduction method. The materials were characterised by a number of techniques which confirmed the presence of Cu2O in contact with the TiO2. Pure TiO2 alone was not active for the simultaneous photocatalytic removal of nitrate and oxalic acid under conditions employed, however, photocatalytic activity was observed for TiO2 and TiO2/AC in the presence of Cu2O. This may have resulted from suppression of charge recombination via creation of a p-n heterojunction between Cu2O and TiO2. Within the series, 2.5% Cu2O/TiO2 exhibited the best photocatalytic performance with 57.6 and 99.8% removal of nitrate and oxalic acid, respectively, with selectivities of 45.7, 12.4 and 41.9% to NH4+, NO2− and N2, respectively after 3h. For the carbon containing photocatalysts, 2.5% Cu2O/TiO2-2·5AC displayed the highest activity with 42.5 and 96.6% removal of nitrate and oxalic acid, respectively, with 32.7, 11.6 and 55.7% selectivities to NH4+, NO2− and N2, respectively. The highest AC loading tested resulted in selectivity to NH4+ of 21.6 with no NO2− detected, together with an improved N2 selectivity (78.4%) albeit at lower (12.7%) nitrate conversion. Data suggests that Cu2O/TiO2 can be used in the photocatalytic reduction of nitrate and improved selectivity towards N2 can be attained by influencing factors which control the relative rate of oxalic acid consumption.

Challenges in photocatalytic reduction of nitrate as a water treatment technology

Management of ubiquitous nitrate contamination in drinking water sources is a major engineering challenge due to its negative impacts from eutrophication to immediate risk to human health. Several water treatment technologies exist to manage nitrate pollution in water sources. However, the most widely used technologies are phase separation treatments. In this context, nanoscale photocatalysis emerges as a highly promising transformative technology capable of reducing nitrate to innocuous nitrogen with noticeable selectivity. This critical review describes the photocatalytic reduction mechanisms of nitrate towards undesirable products (nitrite, ammonium) and the more desirable product (dinitrogen). The mechanisms are based on the standard reduction potential of each individual species and highlight the contribution of reducing species (e.g. CO2−) radicals formed from different hole scavengers. The strategic use of different pure, doped, and composite nanoscale photocatalysts is discussed on the basis of reduction mechanisms' overall conversion, kinetic rates, and selectivity towards N2. The choice of light source affects pathways and influences by-product selectivity because direct photolysis of N-intermediates, which has been overlooked in the literature. In addition, the re-oxidation of nitrite and ammonia as drawback process is explained. Finally, an exhaustive analysis presents the photocatalytic reduction applications for treating real water matrices and the competing effect of other species. Overall, this critical review aims to contribute to the understanding of the potential application/constraints of photocatalysis in inorganic nitrogen management, and guide researchers towards future efforts required for widespread implementation.

Highly selective and efficient photocatalytic reduction of nitrate in water by a tandem reaction system consisting of Pt/TiO2 and SnPd/Al2O3: A comparative study of the tandem reaction system with a typical semiconductor photocatalyst, SnPd/TiO2

A tandem reaction system consisting of a photocatalyst (Pt/TiO2) and a nonphotocatalyst (SnPd/Al2O3) promoted the reduction of NO3− into gaseous products (mainly N2) under light irradiation (λ>300nm) in the presence of glucose as a hole scavenger. Photocatalytic H2 evolution (2H++2e−→H2) proceeded over Pt/TiO2, and conventional catalytic reduction of NO3− with H2 (NO3−+5/2H2→1/2N2+2H2O+OH−) occurred over SnPd/Al2O3. We optimized the loading amount of Pt on TiO2, the Sn/Pd ratio, the loading amount of SnPd on Al2O3, and the two catalyst dosages. The optimized tandem system gave a high reduction rate of NO3− and a high selectivity for gas (94%) from the photocatalytic reduction of NO3− in water. On the other hand, a typical semiconductor photocatalyst SnPd/TiO2 with an optimized Sn/Pd ratio and an optimized loading amount of SnPd bimetal on TiO2 reduced NO3− about two-thirds as fast as the tandem system and was less selective for gas (70%). The tandem system suppressed the wasted H2 formation, resulting in high light use efficiency for the NO3− reduction (95%), which is defined as the ratio of the number of electrons consumed for NO3− reduction to the total number of electrons consumed for both NO3− reduction and photocatalytic H2 evolution, though the tandem and SnPd/TiO2 systems consumed about the same total number of electrons. The tandem system has two advantages: (i) the Pt/TiO2 and SnPd/Al2O3 subsystems can be separately designed to give highly efficient photocatalytic and catalytic reactions, respectively; and (ii) the reaction rates of photocatalytic and catalytic reactions can be easily controlled by changing the catalyst dosage in the reactor. Those advantages brought about a high reduction rate for NO3−, high selectivity for gas, and high light use efficiency for NO3− reduction in the photocatalytic reduction of NO3− in water.

Denitrification in an integrated bioelectro-photocatalytic system

Since nitrate causes severe ecological and health risks, nitrate contamination of drinking water sources has become one of the most important water quality concerns all over the world. Photocatalytic reduction of nitrate to molecular nitrogen presents a promising approach to remove nitrate from drinking water sources. However, harmful intermediates like NO2−, NO, NO2 and N2O are usually formed, and metal loading or hole scavengers are generally needed to reduce the recombination of photo-generated electrons and holes, which will cause secondary pollution to drinking water. In this work, an efficient, selective and sustainable bioelectro-photocatalytic nitrate-reducing system by utilizing commercial TiO2 nanoparticles P25 as the photocatalyst and bio-electrons from microbial metabolism as the hole scavenger is reported. In this system, bio-electrons extracted from organic substrates in bioanode are transferred to the photocathode through an external circuit for hole quenching. With the utilization of the residual photogenerated electrons, nitrate is completely reduced to nitrogen without accumulation of harmful nitrite or ammonium. The experimental results and the mechanistic analysis using the first-principles density functional theory calculations demonstrate that toxic by-products like nitrite or ammonium will not be accumulated in this system. Thus, this approach has a great potential for sustainable remediation of nitrate-contaminated drinking water sources.

Removal of Nitrate by Photocatalytic Denitrification Using Nonlinear Optical Material

Removal of nitrate from water has been receiving growing attention in water treatment. In this study, we report the photocatalytic denitrification (PCDN) by nonlinear optical (NLO) material, i.e. lithium niobate (LiNbO3). The hydrothermally synthesized LiNbO3 powder could achieve efficient denitrification in water, evidenced by 98.4% nitrate removal and 95.8% nitrogen selectivity at reaction time of 120 min and pH-neutral condition. Based on the first-order kinetics of PCDN, the kinetic constant for LiNbO3 is almost three times as that of conventional TiO2 (P25) under the same conditions. As suggested by the hole scavenger experiments, the LiNbO3 should proceed with photocatalytic reduction of nitrate through direct heterogeneous interaction with electrons at the conduction band of LiNbO3. This may represent a different mechanism from P25, where nitrate is mainly reduced by CO2•- radicals generated by the holes at the valence band. The unique second harmonic generation (SHG) effects of NLO materials enable them to produce more electrons and minimize the electron-hole recombination, which improves the efficiency and stability of the PCDN process. The current study provides a proof-of-concept demonstration of NLO photocatalytic material for more effective nitrate removal in water treatment.

Removal of nitrate and simultaneous hydrogen generation through photocatalytic reforming of glycerol over “in situ” prepared zero-valent nano copper/P25

The photocatalytic reduction of nitrate to nitrogen and the simultaneous production of hydrogen was investigated over copper loaded titania (P25) nanoparticles using glycerol as sacrificial agent and UV-A/Vis radiation. The experiments demonstrated that total nitrogen (i.e., nitrate, nitrite, and ammonia) removal efficiencies over 93% were achieved for initial nitrate concentrations up to 150mg/l. A parallel hydrogen production up to 14μM was recorded. Hydrogen generation was affected by nitrate reduction. The reaction rates were dependent on pH and both glycerol and nitrate starting concentrations in the mixture. However, a linear model can be used to describe the process for low concentration of nitrate and constant pH. The system showed a remarkable photoefficiency in decontamination of nitrate-containing solutions and concomitant hydrogen evolution. This study lays the foundation for the future development of numerical models able to predict the chemical behavior of simultaneous proton and nitrate reduction over solar photocatalytic reforming of organics.

ZnCr2S4: Highly effective photocatalyst converting nitrate into N2 without over-reduction under both UV and pure visible light.

We propose several superiorities of applying some particular metal sulfides to the photocatalytic nitrate reduction in aqueous solution, including the high density of photogenerated excitons, high N2 selectivity (without over-reduction to ammonia). Indeed, ZnCr2S4 behaved as a highly efficient photocatalyst, and with the assistance of 1 wt% cocatalysts (RuOx, Ag, Au, Pd, or Pt), the efficiency was greatly improved. The simultaneous loading of Pt and Pd led to a synergistic effect. It offered the highest nitrate conversion rate of ~45 mg N/h together with the N2 selectivity of ~89%. Such a high activity remained steady after 5 cycles. The optimal apparent quantum yield at 380 nm was 15.46%. More importantly, with the assistance of the surface plasma resonance effect of Au, the visible light activity achieved 1.352 mg N/h under full arc Xe-lamp, and 0.452 mg N/h under pure visible light (λ > 400 nm). Comparing to the previous achievements in photocatalytic nitrate removal, our work on ZnCr2S4 eliminates the over-reduction problem, and possesses an extremely high and steady activity under UV-light, as well as a decent conversion rate under pure visible light.