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The ZnO/g-C3N4 composite was synthesized through facile one step calcination method using urea and zinc acetate dehydrate precursors. A series of techniques, TGA (Thermogravimetric Analysis), XRD (X-ray Diffraction), FTIR (Fourier Transform Infrared), BET (Brunauer–Emmett–Teller) surface area, SEM (Scanning Electron Microscopy), TEM (Transmission Electron Microscopy), XPS (X-ray Photoelectron Spectroscopy), UV–Visible DRS (Diffuse Reflection Spectroscopy), PL (Photoluminescence) and EIS (Electrochemical Impedance Spectroscopy) were used to evaluate the physicochemical and optical properties of composites. In the presence of sacrificial electron donor EDTA, ZnO/g-C3N4 photocatalyst gave better visible light response photocatalytic reduction ability against Cr(VI). The enhanced photocatalytic performance of ZnO/g-C3N4 photocatalyst could be ascribed to the addition of ZnO. The heterojunction effects between ZnO and g-C3N4 result in better photogenerated charge separation and slower e− − h+ pairs recombination, which was confirmed from PL, EIS and UV–Visible DRS. The influence of various factors such as ZnO amount in the composite, synthesis calcination condition, catalytic dosage, initial concentration of Cr(VI), EDTA concentration and solution pH have been optimized for the photocatalytic Cr(VI) reduction. Moreover, ZnO/g-C3N4 composite showed modest stability after five cycle. Furthermore, the reaction mechanisms and pathways for Cr(VI) reduction by ZnO/g-C3N4 were proposed. Highlights Photocatalyst ZnO/g-C3N4 composite was prepared by facile single-step calcination method for Cr(VI) reduction. Prepared composite showed excellent photocatalytic Cr(VI) reduction efficiency. Effective charge transfer ability of the composite was observed. Photogenerated e− − h+ pairs recombination process was decreased. EDTA enhanced the photocatalytic Cr(VI) reduction as hole scavenger. [ABSTRACT FROM AUTHOR]

The removal of organic pollutants like methylene blue (MB) from aquatic ecosystems is an urgent environmental challenge due to its toxicity and persistence. The study presents an eco-friendly, low-cost photocatalytic degradation method using hybrid nanocomposites (NCs) of reduced graphene oxide (rGO) combined with TiO 2 and g-C 3 N 4 (rGO/TiO 2 /g-C 3 N 4). The nanocomposites were synthesized through a green approach using Plectranthus amblycinicus (karpooravalli) leaf extract as a reducing and capping agent. The optical, structural, and morphological properties of the nanocomposites were characterized using various techniques. The characterization studies demonstrated that the nanocomposite has significantly enhanced the light absorption characteristics. Under visible light, the rGO/TiO 2 /g-C 3 N 4 NCs achieved 98.5 % degradation of 20 mg/L MB dye within 120 minutes at an optimal dose of 0.05 g/L and pH 11. Kinetic studies revealed pseudo-first-order behaviour, while response surface methodology (RSM) using central composite design accurately predicted the degradation efficiency. The shorter HOMO-LUMO gap of the rGO/TiO 2 /g-C 3 N 4 nanocomposites, resulting from synergistic effects between rGO and the VB-CB alignment of TiO 2 and g-C 3 N 4 , enhanced visible light absorption, charge transfer, and overall photocatalytic performance. Additionally, the nanocomposites exhibited antimicrobial activity against Bacillus subtilis, Staphylococcus aureus, Vibrio cholerae, Escherichia coli, and Aspergillus ni ger. Phytotoxicity studies using Vigna radiata and Vigna unguiculata demonstrated reduced toxicity and improved plant growth in treated dye water. These findings highlight the potential of rGO/TiO 2 /g-C 3 N 4 NCs for treating textile effluents, with applications in irrigation for public parks and roadside vegetation, promoting sustainable wastewater management. [Display omitted] • rGO/TiO 2 /g-C 3 N 4 was synthesized by a sustainable green synthesis method using plant extracts. • rGO/TiO 2 /g-C 3 N 4 nanocomposite exhibited strong photocatalytic activity. • A CCRD approach achieved a 98.5 % reduction of MB dye under optimal conditions. • The rGO/TiO 2 -g-C 3 N 4 NCs demonstrated remarkable antibacterial performance. • Low phytotoxicity in treated wastewater promoted plant growth. [ABSTRACT FROM AUTHOR]

Photocatalytic reduction is a widely researched method for removing heavy metal ions from water. This study successfully synthesized Zr-based bimetallic UiO-66(Zr/Al) materials via a solvothermal method, incorporating aluminum (Al) into the Zr-UiO-66 lattice. Characterization confirmed successful Al(III) doping without altering the fundamental framework. Among the synthesized materials, UZA-6 exhibited remarkable photocatalytic activity, achieving a 99.25 % removal rate of hexavalent chromium (Cr(VI)) from water within 60 min under simulated solar irradiation. Additionally, the catalyst effectively adsorbed the reduced trivalent chromium (Cr(III)) and maintained a removal rate of 97.73 %, thereby achieving complete removal of Cr element in water. Photoluminescence and electrochemical analyses revealed that the enhanced photocatalytic performance was due to improved separation of photogenerated electron-hole pairs and facilitated charge transfer, attributed to Al doping. This research offers valuable insights into developing effective MOF-based catalysts for water purification, highlighting the potential of UZA-6 for efficiently removing both Cr(VI) and Cr(III) from contaminated water. [Display omitted] • UZA-6 catalyst achieves 99.25% Cr(VI) and 97.73% Cr(III) removal, ensuring comprehensive chromium removal. • Aluminum doping enhances photocatalytic activity by improving electron-hole separation and charge transfer. • UZA-6 shows robust Cr(VI) reduction, effective in diverse water purification scenarios across varying conditions. • Electrons and superoxide radicals drive Cr(VI) to Cr(III) reduction, revealing the mechanism of chromium removal. [ABSTRACT FROM AUTHOR]

Efforts to combat global warming and energy-related issues involve the solar-driven reduction of CO 2 into worthy fuels and substances. However, the stable nature of CO 2 demands high energy input for transformation. CO 2 reduction using semiconductor materials activated by sunlight is gaining attention for its eco-friendly and economically viable nature. Despite progress, many solar-active catalysts for CO 2 photoreduction encounter challenges like low efficiency and uncontrollable selectivity. The commonly used rare earth oxide ceria (CeO 2) has low sunlight absorption, necessitating changes such as metal-nonmetal doping oxygen vacancy creation, the addition of co-catalysts, and the development of binary, ternary, Z-scheme, and S-scheme heterostructures to improve its use in visible light. Although there has been considerable research on CeO 2 modifications, there is a lack of comprehensive study regarding their characteristics and the precise photochemical reduction mechanisms. This review aims to bridge this gap by thoroughly examining recent breakthroughs in CeO 2 -based photo reductants for CO 2 reduction. It focuses on the synthetic techniques of photocatalysts and CO 2 reduction processes, assesses photoactivity enhancement strategies, investigates underlying mechanisms, and addresses the factors influencing CO 2 reduction, efficiencies and selectivity. Finally, the review concludes by offering insights into future challenges and prospects, guiding upcoming research toward sustainable and efficient CO 2 reduction strategies. [Display omitted] • Solar-driven reduction of CO 2 into valuable fuels. • Modifications of CeO 2 to enhance visible light absorption vital for CO 2 photoreduction. • Review recent breakthroughs in CeO 2 -based photocatalysts for CO 2 reduction. • Synthetic techniques, enhancement strategies, and reduction mechanisms. • Insights on future challenges and prospects guide sustainable CO 2 reduction research. [ABSTRACT FROM AUTHOR]

• Ag 2 WO 4 /AgVO 3 composites were prepared via a one-pot, controllable, ligand-free and eco-friendly approach. • Levofloxacin was effectively degraded in Ag 2 WO 4 /AgVO 3 composites. • A reasonable mechanism has been explained for the possible degradation pathway. Energy shortages and environmental pollution are two of the most immediate problems all over the world. Photocatalysis is expanding into energy and environmental applications. In this study, novel visible-light-driven Ag 2 WO 4 /AgVO 3 composite photocatalysts were constructed via a one-pot, controllable, ligand-free and eco-friendly approach and analyzed using different techniques. Under visible light irradiation, photocatalytic behavior of type-II heterojunctions in the degradation of levofloxacin hydrochloride is investigated. Various characterizations showed that Ag 2 WO 4 was successfully loaded onto the AgVO 3 surface, which improved the separation and transfer efficiency of the photogenerated charge carriers. Under optimal experimental conditions, the removal efficiency of levofloxacin reached 0.0194 min-1 for the Ag 2 WO 4 /AgVO 3 composites with a 3 : 5 mass ratio (3-WV), which was 5.87 and 17.64 times that of pure AgVO 3 and Ag 2 WO 4 , respectively. The photocatalytic mechanism of typical type-II heterojunction was discussed. Furthermore, possible photodegradation pathway of levofloxacin was comprehensively determined by LC-MS analysis. This work will provide new motivation for the design and synthesis of simple preparation and highly efficient photocatalysts for environmental purification. [Display omitted] [ABSTRACT FROM AUTHOR]

The removal and detection of heavy metals from wastewater have proven to be challenging due to the limitations of the materials and technologies. Therefore, in this work, we have synthesized novel Z-scheme-based MoSe 2 -modified ZIF-67 by a two-step method and tested it for environmental safety by electrochemical detection and photocatalytic reduction of carcinogenic heavy metal pollutant (hexavalent chromium (Cr (VI)). The nanosheets and polyhedrons-like morphology of MoSe 2 and ZIF-67 were confirmed using Field emission scanning electron microscope (FESEM) and High-resolution transmission electron microscope (HRTEM), respectively. The nanocomposite exhibited superior activity for photocatalytic reduction (∼89% within 30 min) towards Cr (VI) along with the detection (LOD-0.01 µM) with high stability. The superior activity of the MZ67 nanocomposite is attributed to enhanced recombination time (4.65 ns) with respect to pristine ZIF-67 (1.21 ns) as observed from time-correlated single photon counting (TCSPC) studies. The scavenger test and electron paramagnetic resonance (EPR) studies confirmed the Z-scheme of the nanocomposite. The electrochemical sensing for Cr (VI) combined with the photocatalytic reduction, tends to provide a trustworthy tool for wastewater management. [Display omitted] • Synthesis and characterization of novel Z-Scheme MoSe 2 @ZIF-67 (MZ67) nanocomposite. • Photocatalytic reduction of Cr(VI) with high efficiency and reusable property. • Charge transfer mechanism proposed and supported by EPR and scavenger study. • Electrochemical sensor with high stability, low detection limit and good selectivity. [ABSTRACT FROM AUTHOR]

Abstract The N-TiO 2 /g-C 3 N 4 @diatomite (NTCD) composite has been prepared through a simple impregnation method, using titanium tetrachloride as precursor and urea as nitrogen-carbon source. Then the effects of calcination temperature on structure, surface property and photocatalytic activity of the catalysts were investigated. And XRD, TEM, XPS, FTIR and UV–vis diffuse adsorption spectroscopy were used to characterize the obtained powders. The photocatalytic activity of the NTCD was evaluated through the reduction of aqueous Cr (VI) under visible light irradiation (λ > 400 nm). The results demonstrated that the nano-TiO 2 particles ranging from 15 to 30 nm in the crystal of anatase are well deposited on the surface of diatomite in the NTCD-500 which calcined at 500 °C for 2 h. Furthermore, the g-C 3 N 4 with the lay thickness of 0.92 nm was attached to the surface of nano-TiO 2. The N-doped TiO 2 and g-C 3 N 4 doped catalysts could co-enhance response in the visible light region and reduce band gap of NTCD-500 (E g = 3.07 eV). And the NTCD-500 sample exhibited nearly 100% removal rate within 5 h for photocatalytic reduction of Cr (VI) which was higher activity than P25, crude TiO 2 @diatomite and g-C 3 N 4 @diatomite. Graphical abstract Image 1 Highlights • The N-TiO 2 /g-C 3 N 4 @diatomite hybrid photocatalyst was prepared and characterized. • The calcination temperature has significant effect on structure and photocatalytic activity of the catalysts. • The N-TiO 2 /g-C 3 N 4 @diatomite heterostructures exhibit superior Cr(Ⅵ) removal rate under visible light irradiation. • The N-TiO 2 and g-C 3 N 4 work together to enhance the photocatalyst reduction of Cr(Ⅵ). The composite exhibit superior Cr(Ⅵ) removal rate and the calcination temperature has significant effect on structure of the catalysts. [ABSTRACT FROM AUTHOR]

Due to industrialization and human activity, the level of CO 2 emission is increasing day by day which harshens the environment. Thus it is a very urgent need to control environmental pollution by managing the CO 2 level in the atmosphere. The introduction of vacancy or heteroatoms defects in the semiconductor metal oxides is one of the promising factors which improve the activity of catalysts. The defective sites revamp the donor density of metal oxides, thus providing the favorable sites involved in the catalytic reaction. Still, there is a lack of understanding mechanism of the role of oxygen vacancies in photocatalytic and electrocatalytic reactions. In this review, we have outlined the approach to control the oxygen vacancies (V o) concentration in the metal oxides during their growth, and the mechanism of the role of V o defect concentrations involved in the catalytic reactions. Further, we have also presented the idea of the regeneration of oxygen vacancies in the aged catalyst. Moreover, we have also highlighted the role of regeneration of oxygen vacancies involved in the regeneration of electrocatalytic activity of the metal oxides towards CO 2 reduction. Lastly, we have reviewed the future scope and challenges of tuning defects and their contribution to the catalytic reaction. Electrochemical, photocatalytic, and photoelectrochemical reduction of CO 2 on metal oxide catalyst. [Display omitted] • The approaches to control the concentration of V o in the metal oxides during their growth and the role of V o defect concentrations involved in the catalytic reactions is discussed in detail. • The mechanism pathway for photocatalytic, electrocatalytic, and photo electrocatalytic based on metal oxide nanostructures is summarized. • The role of oxygen vacancy in regeneration of catalytic activity of catalyst is summarized. • The future scope and challenges of tuning defects and their contribution to the catalytic reaction have been reviewed. [ABSTRACT FROM AUTHOR]

Uranium extraction from seawater has attracted increasing attentions for nuclear raw material to support the sustainable development of nuclear power plants. However, it is still a grand challenge to overcome the high salinity background and ultra-low uranyl concentration. Herein, we successfully achieved Fe-N x configurations embedded in graphitic carbon nitride (FeN x /g-C 3 N 4) through one-step pyrolysis strategy. Our density function theory (DFT) calculations reveal that the site-isolated FeN x centers are the predominant binding sites for U(VI) species, and visible-light photoexcitation can effectively facilitate the electron escaping from FeN x /g-C 3 N 4 surface relative to pure g-C 3 N 4 , which is consequently favorable for electron transfer in the photoreduction conversion of U(VI) to U(IV). Consistent with the theoretical results, the obtained FeN x /g-C 3 N 4 (w (Fe-MOFs): w (g-C 3 N 4) = 2:1) delivers remarkably higher reduction activity with the conversion efficiency of 99 % and rate constant of 0.091 min−1, almost 9.1 and 12.5 times faster than those of g-C 3 N 4 and TiO 2 catalysts, respectively. The results showed that the introduction of FeN x could effectively activate g-C 3 N 4 catalysts for significantly broadening the absorption range of g-C 3 N 4 to visible light, inhibiting recombination of the photogenerated e--h+ and further facilitating the reduction of U(VI). It is worthwhile to mention that FeN x /g-C 3 N 4 maintains a high level for the extraction of uranium from seawater, endowing the metal-N configurations embedded g-C 3 N 4 as a kind of promising candidate for the sustainable conversion of radionuclides. [Display omitted] • FeNx/g-C3N4 was synthesized via one-step pyrolysis strategy. • FeNx/g-C3N4 with outstanding performance for photocatalytic reduction uranium. • DFT calculations reveal that the FeNx sites are the predominant binding sites. • FeNx/g-C3N4 can effectively extract U(VI) from seawater with high electrolyte ions. [ABSTRACT FROM AUTHOR]

Herein, the nitrogen-doped indium oxide (N-In 2 O 3) photocatalyst was confirmed to be highly active and stable for photocatalytic reduction of CO 2 to methanol in an aqueous solution at ambient conditions. The efficiency of N-In 2 O 3 in producing methanol can be flexibly improved by tuning the nitrogen doping content. The highest formation rate of methanol reaches to 394 μmol g cat -1 h-1, with a methanol selectivity of 63%, at a nitrogen doping content of 3.74%. Nitrogen doping generates mid-gap energy states and reduces the bandgap of In 2 O 3 , thus boosting photon absorption and electron-hole separation. Nitrogen doping creates more oxygen vacancies on In 2 O 3 , thus forming more active sites for CO 2 adsorption and conversion. Nitrogen doping also enhances the activity of the surface frustrated Lewis pairs (SFLPs), which further promotes CO 2 adsorption and activation. The multiple-role of nitrogen doping results in the highly active and stable photocatalytic reduction of CO 2 to methanol. [Display omitted] • N-doped In 2 O 3 is prepared by simple discharge-enhanced doping at low temperature. • N-doped In 2 O 3 causes a CO 2 photoreduction with high methanol selectivity. • The methanol yield can be linearly controlled by tuning the nitrogen doping content. • N-doping improves light absorption and electron-hole separation efficiency. • N-doping increases the adsorption and activation of CO 2 with more active sites. [ABSTRACT FROM AUTHOR]

The current study deals with Cr(VI) removal using a polymer-nano metal oxide based composite film under fluorescent light condition. This was prepared by the layer-by-layer coating of chitosan/polyethylene glycol (PEG) blend, polystyrene sulphate (PSS) and nanotitania/nanoalumina mixture respectively on the glass slide. The Taguchi’s orthogonal array ( L 25 ) design was employed for determining the optimal process factors (pH: 6, reaction time: 10 min and initial Cr(VI) concentration: 20 mg L −1 ) and the film preparation factors (dosage of PEG: 0.5 v/v%, dosage of PSS: 0.25 v/v%, dosage of nanotitania–nanoalumina mixture: 95:5 mg L −1 ). The maximum removal capacity observed at the optimal conditions was 278.9 ± 4.3 mg g −1 . The SEM–EDX, XPS, FTIR–ATR spectra confirmed the photocatalytic reduction of Cr(VI) and binding of Cr(III) species on the PSS layer. A 97% regeneration of the film and a cumulative removal capacity of 2467.6 mg g −1 were observed after nine cycles of reuse. This removal capacity for chromium is about twenty fold higher than that reported by any single nanoparticle so far. [ABSTRACT FROM AUTHOR]

The TiO2-mediated photocatalysis process has been successfully used for degrading dye pollutants during past decades. However, the dye degradation efficiency has been proposed to rely only on the concentration of oxygen molecules (through photooxidation pathway). In our current study, the dye ethyl violet (EV) degradation process is prepared under an anaerobic condition. Most interestingly, both photocatalytic reduction and photocatalytic oxidation intermediates are isolated and identified at the first time. Photoreduction intermediates such as benzene, toluene, ethylbenzene, and xylene (BTEX), ethane, and diethylamine are detected by Headspace-GC–MS. Moreover, 18 photodegraded intermediates are also identified and characterized through HPLC–PDA–ESI-MS. The results demonstrate that a novel photodegradation mechanism should be proposed via three competition pathways, including (i) the cleavage of the whole conjugated chromophore structure by photocatalytic reduction, (ii) the cleavage of the whole conjugated chromophore structure by photocatalytic oxidation, and (iii) N-de-ethylation of the chromophore skeleton. [ABSTRACT FROM AUTHOR]

Abstract: The effects on TiO2 (Degussa P25) photocatalytic reduction of Cr(VI) under visible light, using methanol, methanal and formic acid as electron donors were investigated. The results showed that the photocatalytic reduction of Cr(VI) could be encouraged by methanol, methanal and formic acid. The fastest rate of Cr(VI) photoreduction was observed in the presence of formic acid followed by methanal and methanol. Cr(VI) could hardly be reduced by TiO2 without electron donors. The conversion percent of Cr(VI) was 100% using formic acid as electron donors after 80min. For the methanal and methanol systems, the conversion percent of Cr(VI) were 93.62% and 22.69% after 6h, respectively. [Copyright &y& Elsevier]

An advanced photocatalyst heterojunction comprised of 2D sheets of MoS 2 and diamond-like shape ZnO nanoparticles was successfully synthesized via a simple calcination route. The structural properties were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), UV–visible-NIR absorption spectrophotometer, Photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), and Raman analysis. The morphology investigations show the wrapping of MoS 2 nanosheets around the agglomerated ZnO nanoparticles forming a hollow-like shaped structure. Moreover, ZnO/MoS 2 luminescence revealed a remarkable charge carriers' separation. The photocatalytic reduction of CO 2 was performed under UV-light irradiation of a 150 W Hg lamp in three different solvents. ZnO/MoS 2 exhibited high photocatalytic activity towards CO 2 photoreduction into CH 3 OH and minor traces of CH 3 CHO, and C 2 H 5 OH. Methanol was the dominant product with a maximum yield of 170.5 µmol/g. The high photocatalytic activity of ZnO/MoS 2 may be attributed to accumulation of electrons on the surface of 2D-MoS 2 which granted electrons a great mobility that supported the charge carrier's separation. In addition, the hollow-like shaped structure may contribute to greater light absorption through photon refractions inside the shell which increases the photocatalytic performance. [Display omitted] • 2D MoS 2 /ZnO heterostructure was synthesized via simple calcination route. • The MoS 2 /ZnO exhibit superior catalytic activity compared to neat ZnO and MoS 2. • The maximum production yield of CH 3 OH ~170.5 µmol/g in 0.5 M NaHCO 3 solution. • Anion effect and proposed reaction mechanism were investigated. [ABSTRACT FROM AUTHOR]

This work reports an effective effort to indorse the photoreduction of mercury (II) ions (Hg2+) by a developed heterojunction photocatalyst. Nanostructured CuAl 2 O 4 -decorated g-C 3 N 4 was synthesized by MCM-41 and F-127 assisted solution process. The CuAl 2 O 4 nanoparticles were dispersed onto g-C 3 N 4 at 1.0, 2.0, 3.0, and 4.0 wt%. The prepared nanostructures were substantiated large surface areas and mesoporous texture surfaces. TEM observation proved the construction of heterojunctions between CuAl 2 O 4 (28.6 nm) and g-C 3 N 4 networks. The photoreduction of Hg2+ over the 3.0 wt% CuAl 2 O 4 -decorated g-C 3 N 4 below visible-light radiation was attained with a superior rate of 189.4 µmol min−1 compared to 21.95 µmol min−1 for g-C 3 N 4 and 12.95 µmol min−1 for CuAl 2 O 4. The dose optimization of 3.0% CuAl 2 O 4 /g-C 3 N 4. The augmented photocatalytic performance of this novel heterojunction is referred to as confined bandgap and suppression of photogenerated carrier recombination. The sustainable photoreduction of Hg2+ over CuAl 2 O 4 /g-C 3 N 4 for five runs was also confirmed the photostability and regeneration ability. [Display omitted] • CuAl 2 O 4 /g-C 3 N 4 nanostructured heterojunctions synthesized by templated method. • CuAl 2 O 4 augment light-harvesting and carrier separation by bandgap reduction. • Hg2+ photoreduction rate boosted by 9.5 and 12.6 times to pure photocatalysts. • Sustainable photoreduction of Hg2+ after 50 min by tuning of dose. [ABSTRACT FROM AUTHOR]

γ-Hexachlorocyclohexane (γ-HCH, Lindane) is a carcinogen and endocrine-disrupting compound. Lindane's widespread presence in various components of the environment demands efficient methods of its remediation. Photocatalytic reduction (PCR) of γ-HCH, Lindane using P25 (TiO 2) in the presence of Oxalic acid (OA) and Ethylenediaminetetraacetic acid (EDTA) as hole-scavengers (HS) was investigated. Concentrations of OA ≤25 mM could not completely suppress photocatalytic oxidation (PCO). Complete reductive dechlorination of lindane was achieved in the presence of 1 mM EDTA and 1 g/L TiO 2 after 90 min of irradiation at an initial pH of 2.8. Intermediates formed during PCR were analyzed using GC-MS and complete dechlorination of lindane was confirmed by detection of cyclohexene as one of the end-products besides chloride ions. Dichloroelimination and dehydrochlorination followed by hydrodechlorination was the most likely pathway of lindane degradation. The initial pH of the solution greatly influenced the rate and pathway of lindane removal. Reductive dechlorination was favoured at pH 2.8, whereas PCO could not be suppressed at pH 5.1. Complete dechlorination of lindane was also possible under sunlight, although at a much slower rate than that under UV light. PCR of lindane using TiO 2 is not reported so far. [Display omitted] • Photocatalytic reduction of lindane is demonstrated for the first time. • Complete dechlorination in the presence of EDTA confirmed by identification of cyclohexene as an end-product. • Low concentrations of oxalic acid (<25 mM) could not suppress photocatalytic oxidation. • Initial pH influences the rate and pathway of lindane removal. [ABSTRACT FROM AUTHOR]

• Photocatalytic reduction of NO 3 − to N 2 was studied over TiO 2 -based catalysts. • Formate oxidation at h vb + produces CO 2 − that, in turn, reduces NO 3 − to N 2. • Inorganic anions in the medium induce activity loss of the catalysts. • TiO 2 loaded with Ag+ showed performance improvement of c.a. 15 %. Herein we report the study of the photocatalytic reduction of nitrate by TiO 2 in presence of inorganic anions and for TiO 2 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 (h vb +). The observed dependence of the photocatalytic nitrate reduction on the concentration of HCOOH suggests this specie is oxidized at h vb + forming CO 2 − radicals that, in turn, reduces NO 3 − to N 2. The photocatalytic assays in presence of H 2 PO 4 −, SO 4 2−, HCO 3 −, F− and Cl− indicated the surface anionization leading to h vb + blocking and, as consequence, to the decrease of HCOOH oxidation. Indeed, impedimetric data indicated the adsorbed anions on TiO 2 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 (e cb −) with a performance improvement of 15.5 % in respect to the neat TiO 2 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 N 2 close to 100 %. [ABSTRACT FROM AUTHOR]

• Facile synthesis of ZIF-67@MIL-125-NH 2 nanocomposite via in situ modification technique was investigated. • Unusual MOF@MOF structure of ZIF-67@MIL-125-NH 2 nanocomposite was explored. • Surprising performance of ZIF-67@MIL-125-NH 2 nanocomposite in photocatalytic reduction of nitrophenols was studied. Selective photoreduction of nitrophenols comes important for synthesis of pharmaceutical intermediates. Nowadays, metal-organic frameworks (MOFs) play an important role in preparation of photocatalysts because MOFs make shift from using photocatalyst in UV to visible light and upgrade photocatalytic activity and selectivity. In the past, metal and metal oxide nanoparticles were doped physically or chemically into MOFs for enhancement of photocatalytic activity. In this work, for a first time, titanium based metal organic frameworks (MIL-125-NH 2) was post-synthetically modified with different ratios of zeolitic imidazolate framework-67 (ZIF-67), the novelty comes from coating MOFs with MOFs. The crystallinity of the prepared nanocomposite photocatalyst (ZIF-67@MIL-125-NH 2) was interpreted by X-ray diffraction (XRD). The optical properties of the composite were investigated using UV–vis diffuse reflectance spectroscopy (UV–vis DRS). The morphology and particle size was identified by scanning electron microscopy (SEM) and Transmission electron microscope (TEM). The nanocomposite was used for selective photocatalytic reduction of nitro-phenols in visible light irradiation. The nanocomposite showed high photocatalytic activity beside selectivity compared with P25. The effects of reusability of the optimum nanocomposite photocatalyst were investigated. [ABSTRACT FROM AUTHOR]