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Developing stable and efficient catalysts for artificial photoreduction of soluble hexavalent uranium (U(VI)) into less mobile complexes is of considerable value to U enrichment and environmental sustainability. However, the pursuit of high-performance U(VI) photoreduction is greatly plagued by inferior charge separation and utilization for semiconductors. Herein, the multipolar donor-acceptor (D-A) interface and hydroxyl groups are rationally integrated into covalent triazine frameworks (CTFs) for enhancing U(VI) photoreduction without sacrificial agents. Once incorporating phenolic hydroxyl (Ph-OH) groups as electron donors, the targeted CTF-HUST-OH displays high efficiency (∼100 %) for U(VI) removal with a brilliant enrichment capacity (681.15 mg·g−1) under visible light irradiation, superior to most reported metal-free catalysts. Experimental and density functional theory (DFT) results validate that the polarized internal micro-electric field is formed in CTF-HUST-OH with an oriented charge transfer from Ph-OH to triazine units, thus achieving efficient electron separation and utilization. Impressively, the introduced -OH groups promote U(VI) adsorption via increase of pore hydrophilicity, and create reaction sites towards H 2 O 2 production, thereby facilitating in-situ generation of UO 2 O 2 ·4H 2 O(s). This study highlights a new strategy on the molecular-level design of D-A type CTF photocatalysts for efficient uranyl removal and extraction from uranium-bearing aqueous environments. [Display omitted] • Rational construction of D-A type hydroxyl CTFs modulated surface microenvironment. • The Ph-OH serve as sites for U(VI) adsorption and O2 reduction to generate H2O2. • CTF-HUST-OH achieved efficient in-situ U(VI) reduction and enrichment. [ABSTRACT FROM AUTHOR]

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/GdCrO 3 composite was successfully synthesized to photo-catalytically reduce nitrate to N 2 with high selectivity. Compared with TiO 2 (P25), GdCrO 3 , Ag/GdCrO 3 and Cu/GdCrO 3 , 1 wt% Pd/GdCrO 3 achieved higher removal rate of nitrate (98.7%) and selectivity to N 2 (100%). The kinetics constant of 1 wt% Pd/GdCrO 3 was two times higher than that of P25. Even after six cycling runs, 1 wt% Pd/GdCrO 3 still remained high photocatalytic reduction rate of nitrate (95.5%) and selectivity to N 2 (98.4%). Such advantages were not only attributed to the negative conduction band value of GdCrO 3 but also attributed to the co-catalyst effect of Pd. On one hand, nano particles Pd improved the utilization of charge carriers of GdCrO 3 . 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 N 2 O* which would be preferentially transformed into N 2 . Accordingly, high concentration of nitrite accumulated initially could enhance the likelihood of N* encountering nitrite so as to increasing the N 2 selectivity. In addition, electron paramagnetic resonance and hole scavenger experiments demonstrated that both photo-generated electrons and CO 2 − played important role in photocatalytic reduction process, suggesting a different mechanism from P25 where nitrate was mainly reduced by CO 2 −. 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 N 2 of photocatalysts. [ABSTRACT FROM AUTHOR]

A niobate/titanate nanoflakes (Nb/TiNFs) composite was synthesized through a one-step hydrothermal method. Nb/TiNFs displayed a heterojunction structure owing to deposition of a small fraction of niobate onto tri-titanate nanoflakes. Tri-titanate (Na 1.6 H 0.4 Ti 3 O 7 1.7H 2 O) was the primary crystal phase, and the molar ratio of niobate (Na 2 Nb 2 O 6 H 2 O) to titanate was determined to be 1:15.9. Nb/TiNFs showed rapid adsorption kinetics and high adsorption capacity for U(VI) (Langmuir Q max  = 298.5 mg/g). Ion-exchange and surface complexation were the key mechanisms for U(VI) uptake, and the adsorption was further enhanced by the unique tunnel lattice structure of the heterojunction. Moreover, Nb/TiNFs were able to convert U(VI) into its immobile form, UO 2 (s) under solar light through photocatalytic reduction. More than 89.3% of (VI) was transformed into U(IV) after 4 h of solar irradiation (initial U(VI) = 20 mg/L, pH = 5.0). Diffuse reflectance UV–vis absorption spectra and Mott-Schottky plots indicated a narrowed band gap energy of Nb/TiNFs compared to neat TNTs. Density functional theory (DFT) calculation on band structure and density of states further confirmed the heterojunction architecture of niobate and titanate, resulting in offset of the conduction bands for the two phases in the composite material. Therefore, transfer of photo-excited electrons from titanate to niobate leads to inhibition of recombination of the electron-hole pairs. In addition, the trapping of uranium in the tunnel lattice of titanate and niobate heterojunction prevents re-oxidation of U(IV) to U(VI), thus achieving long-term immobilization of uranium. Remobilization tests indicated that only 18.7% of U(VI) was re-oxidized to U(VI) and almost no U dissolved into the aqueous phase when exposed air for 90 days. The new material is promising for separation and safe disposal of high strength radionuclides in water. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Carbon dots (CD) was coupled with TiO 2 mesocrystals, where CD displayed both the electron collectors and the active sites. • The positive charges on the CD/MT surface favored the selective adsorption of Cr(VI) and rapid desorption of Cr(III). • The selective adsorption-desorption has an obvious promotion on the photocatalytic reduction of Cr(VI) and recyclability. • The CD/MT exhibited activity about 5.4 times higher than the pure TiO 2 mesocrystals during photoreduction of Cr(VI). • It provides a simple and effective adsorption-photoreduction-desorption mechanism for the photo-reduction of Cr (VI). Abstract The photocatalytic reduction efficiency of hexavalent chromium (Cr 2 O 7 2− (Cr(VI)) is suffering from high recombination of photoinduced charges, poor adsorption capacity of Cr(VI), and slow desorption of product trivalent chromium (Cr3+ (Cr(III))) from photocatalyst surface. In this work, carbon dots (CDs) was coupled with TiO 2 mesocrystals (MT), where CDs displayed both the electron collectors and the active sites. During photoreduction of Cr(VI), the as-prepared CD/MT exhibited activity about 5.4 times higher than the pure TiO 2 mesocrystals. The positive charges on the CD/MT surface favored the selective adsorption of Cr(VI) and rapid desorption of Cr(III), which has an obvious promotion on the photocatalytic reduction of Cr(VI) and retention of photoreduction activity. Meanwhile, the CDs coupled on TiO 2 mesocrystals facilitated the separation of photogenerated charges. This work provides a simple and effective adsorption-photoreduction-desorption mechanism for the photocatalytic reduction of Cr(VI). [ABSTRACT FROM AUTHOR]

Although UV and visible lights induced photocatalysis has been well developed in recent years, the full spectrum of UV, visible and NIR lights responsive photocatalysis is still few, which is beneficial for energy utilization and practical application. Herein, we report a new sillenite-type Bi 12 MnO 20 photocatalyst prepared by a facile sol-gel method. Through incorporating the Mn 4+ ions into tetrahedral sites of metastable cubic γ-Bi 2 O 3 to split the 3d orbits of Mn 4+ , the new-produced Bi 12 MnO 20 crystal presents peculiar and strong absorption capability, covering the full spectrum of UV, visible and NIR lights in the range of 200–1300 nm. The DFT calculation further confirms the existence of intermediate band state in the band gap of Bi 12 MnO 20 , which was formed by the hybrid of O 2p and Mn 3d orbits. More importantly, under the irradiation of UV, visible and NIR lights, Bi 12 MnO 20 product exhibits excellent photocatalytic reduction activity for Cr(VI), which is mainly due to the relatively good charge separation enhanced by unique electronic structure of the Bi 3+ 6s 2 lone pair, the suitable band positions and the introduction of intermediate band state. In addition, the Bi 12 MnO 20 specimen also displays good visible light driven photocatalytic oxidation property for acid red G, which is mainly caused by h + and O 2 − species. The as-prepared Bi 12 MnO 20 semiconductor would provide a new potential to fulfill the full spectrum responsive photocatalysis. [ABSTRACT FROM AUTHOR]

A novel Mn 3 O 4 @ZnO/Mn 3 O 4 composite was designed to remove Cr (VI) and Cr (III) from water by concurrent photocatalysis and adsorption. The Mn 3 O 4 @ZnO photocatalyst with core-shell nano-sphere structure, was first fabricated by precisely controlled process using a mild hydrothermal method combined with atomic layer deposition (ALD). The wurtzite ZnO layer was uniformly deposited on hausmannite Mn 3 O 4 surface, which formed a typical II-type heterojunction, separating the photo-generated electron-hole pairs effectively. Hence, rapid Cr (VI) reduction by Mn 3 O 4 @ZnO under simulated sunlight irradiation was achieved at 95.3% in 110 min. The pure Mn 3 O 4 as adsorbent could subsequently adsorb the reduced Cr (III) from aqueous solution. Noticeably, the total Cr removal efficiency was enhanced to 92.0% within 70 min by concurrent photocatalysis and adsorption compared to 88.8% even within 120 min in the separate two processes. Mechanism exploration proposed that more active sites on Mn 3 O 4 @ZnO surface would be released for continuous photocatalytic reduction of Cr (VI) after the transfer of reduced Cr (III) from Mn 3 O 4 @ZnO onto Mn 3 O 4 surface. In addition, the synergy of photocatalysis and adsorption on Cr removal was the strongest at pH = 6.0 and the highest removal efficiency of 96.0% was realized within 70 min. The outstanding synergistic effect of photocatalytic reduction and adsorption makes the innovative Mn 3 O 4 @ZnO/Mn 3 O 4 composite a promising candidate for Cr remediation in aquatic environment. [ABSTRACT FROM AUTHOR]

Frequent industrial discharge of various contaminants such as heavy metals into water resources has caused severe environmental damage. In this study, a unique porous corallite-like nanocomposite (SPNH-MOSF@SnS 2 ) was successfully fabricated via surface modification of visible-light-driven photocatalyst (SnS 2 ) and chelating ligand (spirobenzopyran derivative, SPNH) on macroporous ordered siliceous foam (MOSF). In our approach, SnS 2 was selected as the photocatalyst due to its high visible light induced photocatalytic activity. SPNH was modified because it could selectively chelate soluble Cr (III) when exposed to ultraviolet light. This unique nanocomposite could be used for highly efficient reduction and removal of hexavalent chromium [Cr (VI)] from wastewater, especially under the mildly acidic condition. The results indicate encouraging applications of this as-prepared new nanocomposite for treating Cr (VI) containing wastewater. [ABSTRACT FROM AUTHOR]

Photocatalyst is widely applied in environmental remediation and energy conversion. Appropriately engineered band structures of semiconductor photocatalysts are beneficial for enhancing surface reactions under light irradiation. Exposing the highly reductive facets of TiO 2 crystals has been recognized as an efficient approach to promote photocatalytic reduction reaction. However, there is no report about the application of one-step solvothermal reaction for the synthesis of the TiO 2 crystals with (101) facets and in-situ doping. In this work, non-stoichiometric anatase TiO 2 microspheres with designed (101) facets were successfully synthesized by using one-step solvothermal reaction. The prepared non-stoichiometric anatase TiO 2 microspheres with designed (101) facets exhibited a great photocatalytic activity for H 2 evolution with a reaction rate of 3.4 times faster than that of anatase TiO 2 that was neither etched nor doped. The (101) facets of anatase TiO 2 were found to be able to generate and transmit more reductive electrons to promote the H 2 evolution in the photocatalytic reduction reaction. With the femtosecond time-resolved diffused reflectance measurement, the roles of self-doping Ti 3+ as the photogenerated electrons trapping and (101) facets were further elucidated. Our findings might provide a new opportunity to develop an efficient, cost-effective and promising TiO 2 -based catalyst for enhanced photocatalytic H 2 production. [ABSTRACT FROM AUTHOR]

Bismuth yttrium oxide (BiYO 3 ) photocatalysts doped with different Cu amounts were synthesized via a hydrothermal method, characterized and applied for the photocatalytic reduced CO 2 to formic acid under the visible light irradiation. The particle size of Cu/BiYO 3 was smaller than that of BiYO 3 , and the surface area of BiYO 3 was increased from 6.75 m 2 /g to 18.64 m 2 /g when the Cu doping amount of was 2.0%. The FT-Raman results reveal the formation of oxygen vacancies after doping with Cu, which suppressed the charge recombination, and the electrochemical impedance spectroscopy (EIS) proved that the Cu/BiYO 3 has a better electronic transmission capacity. The HCOOH amount of photocatalytic reduction of CO 2 was 2.04 μmol /mL by using 2.0% Cu/BiYO 3 as photocatalyst, which was 2.2 times than that of BiYO 3 . The highly improved performance of the 2.0% Cu/BiYO 3 can be ascribed to the increased surface area, increased light absorption, and efficient charge separation. [ABSTRACT FROM AUTHOR]

Tungsten oxide nanowires (WO 3−x) with rich oxygen vacancies (OVs) were fabricated through a facile hydrothermal method, which had both high adsorptive capability and photocatalytic activity. 95.1% of total U(VI) (C 0 = 10 mg/L) was removed by WO 3−x at pH 5, and 79.9% was transformed to U(IV) to achieve reductive immobilization after photocatalysis under simulated solar light. Band structure and optical characterizations indicated WO 3−x had narrower band gap energy, but higher charger carrier separation and transfer rates compared with conventional WO 3. Density functional theory (DFT) calculations further demonstrate the spin polarization state electrons of W 5d in WO 3−x due to the construction of OVs, thus greatly inhibiting recombination of electron-hole pairs. In addition, the electron density increases in WO 3−x and the photogenerated e – in the conduction band of WO 3−x has higher reduction ability than WO 3 , leading to more efficient electron transfer from WO 3−x to UO 2 2+ after photo-excitation for U(VI) reduction. [Display omitted] • WO 3−x with rich oxygen vacancies show high adsorptive and photocatalytic properties. • U(VI) was efficiently reduced to U(IV) by WO 3−x via photocatalysis under solar light. • OVs induce spin polarization of electrons in WO 3−x and inhibit recombination of e – –h+. • The band and electronic structures of WO 3−x were regulated after OVs construction. • Closer W 5d d-band center to Fermi level leads to high adsorption affinity to UO 2 2+. [ABSTRACT FROM AUTHOR]

Toxic hexavalent chromium reduction to less toxic trivalent chromium was evaluated using a solar driven photocatalytic system, Fe(III)/UV, in the presence of organic sacrificial agents. The photocatalytic reduction experiments were conducted in a lab-scale tubular photoreactor with compound parabolic collectors under simulated solar radiation. The effect of parameters such as iron (1–12 mg L −1 ) and citric acid (0.058–3.840 mM) concentrations, pH value (3.0–8.0), temperature (15–40 °C), UVA irradiation source and initial Cr(VI) concentration (1, 10, 20, 40 mg L −1 ) on the process efficiency was analyzed, and also the addition of other organic ligands like oxalic acid, maleic acid and EDTA. The presence of citric acid proved to enhance the Cr(VI) reduction by Fe(III)/UV due to the formation of Fe(III)-Citrate complexes, providing a quicker pathway for ferric iron regeneration in the presence of UV–vis light. The organic ligands proved to act also as sacrificial agents of reactive oxygen species formed, avoiding the Cr(III) re-oxidation. The catalytic activity of the organic ligands in the Cr(VI) reduction by Fe(III)/UV followed this order: citric acid > oxalic acid > EDTA > maleic acid. The best Cr(VI) reduction (99% in 15 min) was achieved with citric acid in a Cr(VI):Citric acid molar ratio of 1:3 at pH 5 and 25 °C. Finally, the photocatalytic reduction of Cr(VI) present in a real effluent was achieved after 30 min, demonstrating the potential of the Fe(III)/UVA-vis/citric acid system for the treatment of Cr(VI) containing wastewaters. [ABSTRACT FROM AUTHOR]

Highly efficient photocatalytic reduction of environmental pollutants requires the enrichment of photogenerated electrons on the photocatalyst’s surface. Thus, proper material design and modification are needed to efficiently separate photogenerated electron/hole pairs and achieve their oriented migrations for the enrichment of photogenerated electrons on their surface. In this work, a modified photo-deposition process was developed which successfully deposited silver nanoparticles selectively on {1 0 1} facets of TiO 2 nanocrystals with co-exposed {0 0 1}/{1 0 1} facets. The synergistic effect of crystal facet engineering and the selective deposition of silver nanoparticles on {1 0 1} facets largely enhanced the separation of photogenerated carriers and enriched the presence of photo-generated electrons onto the surface of TiO 2 to a net negative-charged surface. A strong photocatalytic reduction capability of the sample was demonstrated by its superior photocatalytic reduction activity on aqueous nitrate under a simulated solar illumination. The removal ratio of aqueous nitrate reached ∼95%, and most of the reduction product was the desirable N 2 with the selectivity over 90%. These TiO 2 nanocrystal with co-exposed {0 0 1}/{1 0 1} facets and silver modification on {1 0 1} facets could also effectively remove both nitrate and various organic pollutants from water simultaneously. [ABSTRACT FROM AUTHOR]

Highly active CuO-modified TiO 2 (Degussa P25) photocatalysts were prepared by an impregnation method. Efficient and rapid degradation of polybrominated diphenyl ethers were achieved on CuO/TiO 2 photocatalysts. Both TiO 2 and CuO/TiO 2 yielded a rapid photocatalytic reduction of decabromodiphenyl (BDE209). However, the photo-reductive degradation of 2,2′,4,4′-tetrabromodiphenyl ether (BDE47) was impossible on TiO 2 , but became fast on CuO/TiO 2 . Moreover, the photo-reductive degradation of BDE47 on CuO/TiO 2 needed a short induction time period (20 s) to initiate the reduction. A mechanism was proposed for the enhanced photo-reductive degradation of BDE47 on CuO/TiO 2 . During the induction time period, the CuO clusters trapped electrons from TiO 2 to form Cu 2 O as confirmed by XPS analysis. Further surface photovoltage and phase spectroscopic analysis and flatband potential measurements were conducted for TiO 2 , CuO/TiO 2 and Cu 2 O/TiO 2 . In the new mechanism, a “switching reduction potential by the valence state of copper” concept was proposed. Because of the higher reduction potential of Cu 2 O than CuO and TiO 2 , the in-situ composition change led to a Fermi level shift to a more reductive energy for injecting electrons to BDE47, resulting in the initiation of the photocatalytic reduction of BDE47 on CuO/TiO 2 . The proposed concept was useful to design and regulate photocatalysts for reductively degrading persistent pollutants. [ABSTRACT FROM AUTHOR]

Anatase TiO 2 with exposed {0 0 1} facets (denoted as T001) is becoming one of the hotspots in photocatalytic field due to the highly reactive {0 0 1} facets. Nowadays, to further extend the applications of T001 in visible region, researchers are struggling to develop T001-based visible-light-responsive photocatalysts. In this paper, for the first time, CdSe quantum dots (QDs)-decorated T001 (denoted as CS-T001) was synthesized successfully via a facile method and demonstrated as a highly efficient and stable photocatalyst for reduction of nitro aromatics under visible light irradiation. Besides the obviously extended light absorption in visible region, the decoration of CdSe QDs onto T001 would remarkably improve the transfer and separation efficiency of photogenerated charge carriers, resulting in the much higher activity of CS-T001 as compared with pure T001 and CdSe QDs. Serving as the accepted sites for photoelectrons generated from CdSe QDs, the substrate T001 also plays a vital role. First, T001 offers highly active reaction sites due to the much higher surface energy of {0 0 1} facet than that of {1 0 1} facet. Second, compared with CdSe QDs-decorated anatase TiO 2 with exposed {1 0 1} facets (denoted as CS-T101), CS-T001 can generate electrons with stronger reducibility to participate in the photocatalytic reduction process. Third, the aggregation of T001 nanosheets gives rise to the porous structures with slit-like pores, providing efficient transport pathways to reactant and product molecules. Fourth, CS-T001 possesses much higher separation efficiency of photogenerated charge carriers as compared to CS-T101. We believe that our work could not only provide a facile method for fabricating novel QDs-decorated T001 photocatalysts but also help us to realize the synergy between decoration of QDs and exposure of TiO 2 {0 0 1} facets during the photocatalytic reaction process. [ABSTRACT FROM AUTHOR]

The photocatalytic reduction of rhodium(III) chloro–aqua complexes, [RhCl n (H 2 O) 6− n ] 3− n ( n = 0–6), was carried out employing formic acid, ethanol and sucrose as hole scavengers or sacrificial reducing agents (SRA). The investigation was conducted in air equilibrated titanium dioxide (TiO 2 ) suspensions at 25 °C and pH 1employing UV light within a closed-loop flow-through reactor. Varying the sodium chloride concentration, according to speciation data, individual solutions of rhodium(III) chloro–aqua complexes were prepared at those Cl − -concentrations coinciding with the maximum of a specific species, and to that regard the photocatalytic reduction behaviour of Rh(III) was related to the complex present in greater abundance. The fastest photocatalytic reduction rate was observed for those solutions having neutral and anionicrhodium(III) chloro–aqua complexes dominant in solution. No photocatalytic reduction, of any of therhodium(III) chloro–aqua complexes, was effected in the absence of an organic SRA, which is in contrast to [PdCl n (H 2 O) 4− n ] 2− n ( n = 0–4) and [PtCl n (H 2 O) 4− n ] 2− n ( n = 0–4) that do show photocatalytic reduction in the absence of an added organic SRA. At low concentrations sucrose was found to be a superior SRA compared to both ethanol and formic acid. This behaviour is attributed to the structural differences of the SRAs as sucrose has more oxidizable electron donor sites, in the form of hydroxyl groups, compared to both ethanol and formic acid. However, at higher concentrations ethanol was found to be a more effective SRA than both formic acid and sucrose. This is due to coagulation of the photocatalyst (TiO 2 ) setting in at higher sucrose concentrations, which causes the photocatalyst to settle out from suspension. [ABSTRACT FROM AUTHOR]

Highlights: [•] [PtCl n (H2O)4−n ]2−n (n =0–3) is reduced in the absence of a sacrificial reducing agent. [•] [PtCl4]2− is not reduced in the absence of a sacrificial reducing agent. [•] Oxygen impedes the photocatalytic reduction of Pt(II)-chloride complexes. [ABSTRACT FROM AUTHOR]

Highlights: [•] Fe-doped anatase TiO2 was synthesized by two-step hydrothermal method. [•] Quantum yield of ammonia photogenerated is 3.84 times higher than pristine TiO2. [•] Photogenerated radical species like O2 − and OH were detected. [•] Quantum yields depend on the partial pressure of nitrogen in the reaction. [•] Possible nitrogen photofixation mechanism based on electron transfer was proposed. [ABSTRACT FROM AUTHOR]

Highlights: [•] [PdCl4]2− is successfully reduced in the absence of a sacrificial reducing agent. [•] Only rutile reduces [PdCl4]2− in the presence and absence of dissolved O2 (from air). [•] Oxygen impedes the photocatalytic reduction of Pd(II)-chloride complexes. [ABSTRACT FROM AUTHOR]

Highlights: [•] N-doped TiO2 nanocrystals are solvothermally synthesized using HNO3 as the N source. [•] High specific surface area and remarkable visible light-absorbing ability. [•] High photocatalytic activity for the reduction of Cr(VI) in water. [•] Catalyst dosage and Cr(VI) concentration affect the efficiency of Cr(VI) reduction. [•] Cr(VI) is photocatalytically reduced to Cr(III). [ABSTRACT FROM AUTHOR]

Highlights: [•] A system photoreduction process on the principle of dye-sensitized solar cells. [•] Light absorption and charge separation are performed in the DSC zone. [•] Cr(VI) reduction with transferring electrons was conducted at catalysis zone. [•] The high efficiency reactor system can handle Cr(VI) and phenol concurrently. [•] The system affords a platform to realize the environment improvement. [ABSTRACT FROM AUTHOR]

Abstract: Photoreduction of Cr(VI) was successfully achieved on WO3 doped TiO2 nanotube (NT) arrays in the presence of citric acid. WO3 doped TiO2 NT arrays were fabricated by annealing anodic titania NTs that were preloaded with peroxotungstic acid. Driven by electrostatic force, the negatively charged peroxotungstic acid sol uniformly clung to the positively charged titania NT arrays, causing a solid solution of WO3 and TiO2 after annealing. The citric acid plays an important role in the photoreduction of Cr(VI): (i) it works as a sacrificial electron donor to deplete the photogenerated holes from the excited TiO2; and (ii) it takes part in the redox with Cr(VI) under UV illumination because of its electron rich property. The photochemical-reduction rate of Cr(VI) in citric acid under simulated solar light was 6.9μg/Lmincm2. Subtracting the part mentioned above, the reduction rate of Cr(VI) due to photogenerated electrons from excited photocatalysts increased from 8.3μg/Lmincm2 on TiO2 NTs to 31.6μg/Lmincm2 on WO3/TiO2 NTs containing 1at% of W. The net Cr(VI) reduction rate on WO3/TiO2 NT arrays is 3.76 times that on the unmodified TiO2 NTs. Since both WO3 and TiO2 can be excited by UV light, the enhanced photoactivity of WO3/TiO2 is attributed to the increased probability of charge–carrier separation and the extended photo-response spectrum in visible light region due to the doping of WO3 (band gap: 2.6eV). [Copyright &y& Elsevier]

Abstract: The feasibility of heterogeneous photocatalysis for the treatment of dicyanoargentate complexes in solution using titanium dioxide was investigated. The best results were obtained in the presence of oxygen, as the simultaneous deposition of metallic silver on the catalyst and oxidation of released cyanide ions to cyanate species was achieved. It is proposed that O2 plays a dual role in the reaction: it supports the reduction of the metal acting as intermediate in the transfer of electrons and acts as reagent in the oxidation of released cyanide to cyanate species. The influence on the kinetics of the addition of methanol was studied. In anoxic conditions the rate of silver reduction was increased, what is attributed to the effectiveness of methanol as hole scavenger and its ability to form reducing radicals, whereas the oxidation of released CN− was inhibited. On the contrary, in aerobic medium the presence of the alcohol had a detrimental effect on the metal reduction but no cyanide accumulation was produced. The photocatalytic treatment of an industrial spent silver plating bath was carried out. In anoxic conditions, the recovery of silver upon deposition on the catalyst as Ag0 was achieved. As the large amount of organic matter in the solution inhibited the oxidation of cyanide ions, a two-step procedure is proposed for the overall treatment of those wastewaters. [Copyright &y& Elsevier]

Abstract: Ru doped anatase supported on silica was prepared by solid-state dispersion method and examined for the photocatalytic reduction of carbon dioxide in aqueous medium at ambient conditions. To assist in interpreting the photocatalytic behaviour of Ru-TiO2/SiO2, reference systems consisting of Ru doped TiO2 and TiO2 supported on SiO2 were also analyzed and the conditions were optimized. Ru/TiO2 photocatalysts with metal loadings of 0.1, 0.3, 0.5 and 1.0wt% were prepared by impregnation method and a series of TiO2/SiO2 catalysts with low TiO2 (1, 3, 5 and 10wt%) contents were prepared by solid-state dispersion method. The photocatalysts were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), UV–vis DRS, FT-IR and Raman spectroscopy. The results showed that TiO2 particles with Ru ions have higher photocatalytic activity than undoped TiO2 and the optimum Ru loading was found to be 0.5wt%. Nevertheless, the yield increased notably when TiO2 was supported on SiO2. This strong enhancement suggests that in 10wt% TiO2/SiO2 the efficiency of charge separation is strongly influenced through the presence of Tih name="sbnd" />Si bridging bonds. On the contrary, Ru-TiO2/SiO2 has no significant improvement in activity over TiO2/SiO2 except that it shows nearly quadruple times higher activity for the formation of methanol than Ru/TiO2. The difference in the photocatalytic activity is related to its physico-chemical properties. [Copyright &y& Elsevier]

Abstract: The photocatalytic reduction of Cr(VI) to the less toxic Cr(III) is presented in the presence of the polyoxometalates (POM) PW12O40 3− or SiW12O40 4− as photocatalyst and an organic substrate (salicylic acid or propan-2-ol) as electron donor. Cr(VI), as dichromate, is reduced to Cr(III), according to the 6:1 stoichiometry of PW12O40 4− versus Cr2O7 2− indicated from experiments in the dark. Increase of POM or salicylic acid (SA) concentration accelerates, till a saturation value, both the reduction of metal and the oxidation of the organic, suggesting that these two conjugate reactions act synergistically. The photocatalytic action of POM is not so important in the case of highly concentrated solutions of organics that exhibit direct photochemical reduction of Cr(VI), i.e. propan-2-ol (i-prOH), while it becomes important at low concentrations of i-prOH, especially for organics that do not react directly photochemically with Cr(VI), such as SA. Increase of Cr(VI) concentration enhances consumption of SA and Cr(VI) till an optimum value, due to inner filter effect. The method is suitable for a range of chromium concentration from 5–100ppm achieving complete reduction of Cr(VI) to Cr(III) up to non-detected traces (>98%). The presence of oxygen does not influence the efficiency of SA and Cr(VI) consumption. In contrast to the semiconductor-based heterogeneous photocatalysis, the POM-based homogeneous process seems superior in the frame that: (i) it remains catalytic throughout illumination by providing more active sites and (ii) among the two POM used, the one that is more efficient in the degradation of the organic, that is PW12O40 3− compared to SiW12O40 4−, is also more efficient in reducing Cr(VI), due to a kinetic effect, and a compromise is not needed. [Copyright &y& Elsevier]

Using the polyoxometallate anions (POM) PW12O403-, SiW12O404-, H2W12O406- or P2Mo18O626- as photocatalysts and propan-2-ol as sacrificial electron donor, Pd2+ can be reduced and recovered in metallic form. The method leads to very low final palladium concentrations (<0.2 ppm) while the soluble POM catalyst is self-separated from the pure precipitated metal that is obtained, retaining its catalytic function.The process is efficient in both one-pot and two-pot system. However, reduced tungstates of the formula XW12O40n-, X = P, Si or H2 that react rapidly with oxygen are preferably photochemically produced in situ in a one pot system, where propan-2-ol/POM/Pd2+ species co-exist. On the other hand, the 2-equivalent reduced P2Mo18O626- is preferably used in a two-pot system, pre-formed upon photolysis of a propan-2-ol/POM system and in turn serves as an easily kept electron storage (since it is inert against reoxidation by oxygen) amenable to reduce Pd2+ ions at will.Some novel results are marked concerning the environmental photocatalysis with POM: i) Upon photolysis of a one-pot system where propan-2-ol/POM/Pd2+ species co-exist and under the same conditions, the rate of photocatalytic reduction of palladium follows the photoxidizing ability of POM (PW12O403->SiW12O404->H2W12O406-). That is, POM catalysts that are more efficient in photo-oxidative degradation of organic compounds are also more effective in reductive recovery of palladium. ii) Selectivity in recovery of palladium among mixture of non-noble metal ions (Cu2+ and Ni2+), can be achieved even when they are in more than 10-fold excess. [Copyright &y& Elsevier]

Carbon dioxide was photocatalytically reduced to produce methanol in an aqueous solution using 254 nm UV irradiation. Titania and Cu-loaded titania were synthesized by an improved sol–gel method using a homogeneous hydrolysis technique. The grain size of TiO2 and Cu/TiO2 were uniform and average diameters were approximately 20 nm. Photocatalytic reduction was conducted in a quartz reactor with a UV lamp irradiating at the center. XPS analysis reveals that Cu 2p3/2 is 933.4 eV indicating primary Cu2O species on the TiO2 supports. EDX and XPS revealed that most copper clusters were on the TiO2 surface. The optimum amount of copper loading was 2.0 wt.% for the highest dispersion among catalysts. The methanol yield of 2.0 wt.% Cu/TiO2 was 118 μmol/g following 6 h of UV illumination. The yield was much higher than those of sol–gel TiO2 and Degussa P25, whose yields were 4.7 and 38.2 μmol/g, respectively. The methanol yield reached a steady-state 250 μmol/g after 20 h of irradiation. Experimental results indicated that the methanol yield was significantly increased by adding NaOH. The caustic solution dissolved more CO2 than did pure water. In addition, the OH− in aqueous solution also served as a strong hole scavenger. The redistribution of the electric charge and the Schottky barrier of Cu and TiO2 facilitates electron trapping via supported Cu. The photocatalytic efficiency of Cu/TiO2 was markedly increased because of the lowering the re-combination probability for hole–electron pairs. The highest quantum and energy efficiencies achieved were 10 and 2.5%, respectively. [Copyright &y& Elsevier]

The photocatalytic reduction of the pollutant Hg(II) salts using a TiO2-photocatalyst (Hombikat UV100) was studied in aqueous air-equilibrated suspensions of 2 g TiO2 per dm3 of Hg(II) chloride solution (100 ppm) and irradiated by a medium pressure (UV–VIS) mercury lamp. The photoreduction of mercury salts was studied as a function of irradiation time, pH of the suspension, initial Hg(II) concentration and mass of the semiconductor in the suspension. The activity of Hombikat UV100 was compared with the catalytic activity of the “traditional” TiO2-photocatalyst (Degussa P25). The reduction was found to be first-order in [Hg(II)]. An optimum mass of Hombikat UV100 (2 g per dm3 of suspension), where a maximum light absorption by TiO2, was ascertained. The effect of oxygen on the photoreduction was investigated by experiments using air-equilibrated or nitrogen-purged suspensions. The results showed that the process is more efficient in the absence of oxygen. Using 20% (v/v) methanol aqueous suspension, increased the photoreduction. Changing the anion of the mercuric salt by using nitrate instead of chloride, also increased the extent of photoreduction. Hombikat UV100 was more efficient than Degussa P25, possibly because of the higher surface area of the former catalyst. [Copyright &y& Elsevier]

We report the first example of covalent organic framework (DHBD-TMT) linked by unsubstituted olefin-linkages for selective loading, chemical reduction and photocatalytic reduction of uranium. The unique structures of DHBD-TMT possess all the characteristics to be well suited as a capture platform for selective ligand complexation, efficient chemical reduction and photocatalytic reduction of uranium, thus exhibiting a groundbreaking uranium capture capacity (2640.8 mg g-1). [Display omitted] • Covalent organic framework (DHBD-TMT) as a uranium adsorbent through three synergistic mechanisms. • This is the first example of covalent organic framework for selective adsorption, chemical reduction and photocatalytic reduction of uranium. • DHBD-TMT is very suitable as a capture platform for selective ligand complexation, efficient chemical reduction and photocatalytic reduction of uranium. • DHBD-TMT exhibited a groundbreaking uranium capture capacity. Herein, we report the first example of covalent organic framework (DHBD-TMT) linked by unsubstituted olefin-linkages for selective loading, chemical reduction and photocatalytic reduction of uranium. The unique structures of DHBD-TMT possess all the characteristics to be well suited as a capture platform for selective ligand complexation, efficient chemical reduction and photocatalytic reduction of uranium, thus exhibiting a groundbreaking uranium capture capacity (2640.8 mg g-1). In the dark, DHBD-TMT can effectively adsorb uranium through the hydroxyl groups laced on the skeleton and reduce UVI to UIV in situ, leading to a higher adsorption capacity and selectivity of uranium. At the same time, the synergistic effect of the hydroquinone and triazine units in the extended π-conjugated skeleton significantly improve the photocatalytic activity of DHBD-TMT, and an additional UVI photocatalytic reduction mechanism can occur under visible light irradiation, allowing significantly higher the capacity and faster adsorption kinetics. [ABSTRACT FROM AUTHOR]

• A binary noble-metal-free 2D/2D heterojunction was fabricated by simple electrostatic self-assembly. • The adsorbed indium ions prevent the re-stacking of Ti 3 C 2 nanosheets and ensure the in-situ growth of In 2 S 3 nanoflakes. • The 2D/2D heterojunction has a short charge transfer distance resulting in effective charge transfer. • Its enlarged pore and specific surface area significantly improve the adsorption capacity of Cr(VI). • It can rapidly reduce Cr(VI) under visible light with the first-order kinetic rate constant of 0.730 min−1. The conversion of highly toxic heavy metal hexavalent chromium (Cr(VI)) in the natural environment into low-toxic trivalent chromium (Cr(III)) is one of the research topics of great concern. Herein, a binary noble-metal-free photocatalyst consisting of ultrathin MXene (Ti 3 C 2) and indium sulfide (In 2 S 3) is prepared for ultrafast photocatalytic reduction of Cr(VI) to Cr(III) under visible light. A simple electrostatic assembly and reflow method uniformly coats the In 2 S 3 nanoflakes on the surface of hollow Ti 3 C 2 nanospheres, which effectively boost the separation of charges and thus enhance the photocatalytic performance. Thus, the prepared heterojunction can reduce Cr(VI) to Cr(III) completely within 6 min with an ultrafast rate constant of k = 0.739 min−1. More importantly, the appropriate band structure ensures the stable existence of Cr(III). Therefore, it provides a new insight for economic MXene-based binary photocatalysts for efficient environmental remediation. [ABSTRACT FROM AUTHOR]

• Novel surface functionalization approach for synthesis of Au@CNT@TiO 2 nanocomposite. • CNTs act as electron reservoirs to trap electrons from TiO 2 and Au nanoparticle. • Au@CNT@TiO 2 shows about 7.5 times higher photocurrent generation than the TiO 2. • Au@CNT@TiO2 shows efficient decomposition of industrial toxic compound and ion. Au@CNT@TiO 2 nanocomposite performed as an effective catalyst for the degradation of toxic organic dyes, reduction of p-nitrophenol to p-aminophenol, coumarin molecule to 7-hydroxycoumarin and for the removal of toxic ions Cr(VI). The local volumetric rate of photon absorption and total rate of photon absorption was calculated for quantitative confirmation of the photocatalytic activities. The total rate of photon absorption for Au@CNT@TiO 2 and Au@TiO 2 nanocomposite was almost equal while TiO 2 nanorods had it slightly lower. The calculated optical thickness values were within the range of optimal value (1.8–4.4) for planar reactors for all the catalysts. The higher catalytic activity is attributed to effective photogenerated charge generation, charge separation, and broad-spectrum absorption of solar light. The Au@CNT@TiO 2 nanocomposite exhibits more than two times higher photocatalytic activity as compare to TiO 2 nanorods for the degradation of organic dye. Au@CNT@TiO 2 nanocomposite shows seven times higher photocurrent density as compare to TiO 2 nanorods. [ABSTRACT FROM AUTHOR]

• The controllable atom-thick Bi 2 MoO 6 nanosheets have been achieved by hydrothermal reaction. • Highly Efficient photocatalytic nitrobenzene reduction was achieved on Bi 2 MoO 6 nanosheets. • The photocatalytic activity strongly depends on the thickness of Bi 2 MoO 6 nanosheets. • The nitrobenzene conversion of Bi 2 MoO 6 monolayers is higher than most of common photocatalysts. High efficiency and selectivity is significant for photocatalytic organic transformation. In this work, the efficient photocatalytic reduction of nitrobenzene into aniline is achieved on non-noble metal thickness-tunable bismuth molybdate nanosheets prepared by the simple hydrothermal reaction. The photocatalytic activity of Bi 2 MoO 6 strongly depends on the nanosheet thickness. The Bi 2 MoO 6 monolayer displays remarkably enhanced photocatalytic activity for selective reduction of nitrobenzene than bilayer, multilayers and bulk Bi 2 MoO 6 due to the unique properties of 2D materials with the large fraction of surface atoms and the ultrafast charge separation. The obtained conversion rate of 487.5 μmol g−1. h-1 (>95% conversion and >99% selectivity within 60 min reaction) on Bi 2 MoO 6 monolayers is 5 times higher than that of Bi 2 MoO 6 bulk, far exceeding most of common photocatalysts up to date. This work provides a thickness dependent nanosheet concept in the design of newly highly efficient catalysts for the photocatalytic reduction conversion of nitroarenes to anilines. [ABSTRACT FROM AUTHOR]