Environmental remediation of aqueous nitrate solutions by photocatalytic reduction using Pd/NaTaO3 nanoparticles

Performance of L-Cu&Mn-nZVFe@B nanomaterial on nitrate selective reduction under UV irradiation and persulfate activation in the presence of oxalic acid

A novel nanomaterial (L-Cu&Mn-nZVFe@B) was synthesized and was applied to nitrate selective reduction under UV irradiation and persulfate activation in the presence of oxalic acid. Results denoted the deposition of copper could prompt the nitrate conversion and improve the nitrate conversion significantly. The high nitrate conversion was on account of the formation of galvanic cells accelerating the generation of electrons, in which Fe° acted as anode and Cu° acted as cathode. Meanwhile, the coexistence of Cu₂O and MnO₂ exhibited excellent photocatalytic performance with the obvious improvement of N₂ selectivity because of the formation of heterojunction could boost the generation of CO₂^-. Furthermore, the deposition of manganese could also accelerate the generation of CO₂^- through the activation of persulfate. The conversion of NO₃^- was almost 100 % and the N₂ selectivity could reach 81.57 % by the S₂O₈^2-/UV/L-Cu&Mn-nZVFe@B/H₂C₂O₄ system when the initial nitrate concentration was 100 mg /L, the L-Cu&Mn-nZVFe@B dosage was 6.0 g/L, the H₂C₂O₄ dosage was 15 mmol/L, pH was 5.0, the reaction time was 100 min under 25 °C. Research provides an alternative approach for selective reduction nitrate into nitrogen.

TiO2-based catalysts for photocatalytic reduction of aqueous oxyanions: State-of-the-art and future prospects

Nowadays, an increasing discharge of oxyanions to the natural environment has been attracting worldwide attention. TiO₂-based photocatalysis is regarded as one of the most promising technologies for the conversion of toxic oxyanions (such as chromate, nitrate, nitrite, bromate, perchlorate and selenate) to harmless and/or less toxic substances in contaminated waters. Various types of TiO₂-based catalysts have been developed, and each of them exhibits its own advantages in catalytic reduction of oxyanions. However, the application of these nanostructured TiO₂ in real water bodies remains a challenge, with limitations associated with sunlight harvesting abilities, production costs, reuse stability and exposure risks. Herein, we aim to present a critical review on reported TiO₂-based photocatalytic reduction of aqueous oxyanions, provide a comprehensive understanding of the possible reaction pathways of formed active species, and evaluate the reduction performance of different types of TiO₂-based catalysts. In addition, the impact of operating parameters (such as solution pH, temperature, dissolved oxygen and coexisting substances) on catalytic reduction performance is discussed. Furthermore, the perspectives of TiO₂-based photocatalytic reduction of oxyanions are also proposed.

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.

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 (RuO_x, 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.

Advances in nanomaterial based approaches for enhanced fluoride and nitrate removal from contaminated water

Various nanomaterials for fluoride and nitrate removal from contaminated water.

Superior performance of CuInS2 for photocatalytic water treatment: full conversion of highly stable nitrate ions into harmless N2 under visible light

CuInS₂ exhibits a high record of photocatalytic efficiency in visible light driven nitrate reduction without over-reduction nor H₂ generation.

Enhanced photocatalytic degradation activity for tetracycline under visible light irradiation of Ag/Bi3.84W0.16O6.24nanooctahedrons

In this work, a Ag/Bi_3.84W_0.16O_6.24nanooctahedron composite photocatalyst was successfully synthesizedviaa green method at room temperature using silver nitrate (AgNO₃) as the silver source.