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Direct oxidation of organic pollutants by manganese oxides is appealing for the removal of persistent organic pollutants (POPs) since it requires no chemical dosing. Rapid electron transfer and moderate adsorption are vital in manganese-induced oxidation. In this study, we used perovskite lanthanum manganate (LaMnO3) as a model to explore the relationship between bisphenol A (BPA) removal efficiency and metal–oxygen covalency, which is closely related to electron transfer and adsorption capacity, by introducing other metals or defects at the A-site. X-ray absorption spectra (XAS) and density functional theory (DFT) calculation showed that the charge migration rate and BPA adsorption capacity on manganese oxides increase with the increase of metal–oxygen covalency. The manganese oxides with medium metal–oxygen covalency have the strongest oxidation capability toward BPA. Our work provides new regulatory strategies for enhancing the oxidation ability of manganese oxides to directly decompose organic pollutants via interfacial electron transfer. [ABSTRACT FROM AUTHOR]

Surface acid site regulation of photocatalysts is a promising strategy to improve their performance. Herein, surface acid sites of cadmium sulfide were rationally regulated by cerium doping, which resulted in significantly increased photocatalytic activity for tetracycline hydrochloride (TC-HCl) degradation. The generated Brønsted acid sites were verified to favor the adsorption of organic molecules because of their strong affinity. Meanwhile, Lewis acid sites acted as the active sites for C–C bond cleavage via a nucleophilic substitution process, which was testified by the Fukui function and electrostatic potential. Besides, Ce3+ doping suppressed the recombination of electron–hole pairs, which also boosted the performance of TC-HCl degradation. Moreover, the degradation pathway of TC-HCl was deduced based on theoretical calculations and HPLC-MS results. The toxicity of pollutants and intermediates was also evaluated. This work provided new insight into the rational design and preparation of highly efficient photocatalysts for environmental purification. [ABSTRACT FROM AUTHOR]

Cobalt-modified rhenium disulfide nanosheets rich in defects, obtained by following an ingenious atom substitution strategy, exhibited boosted HER performance. The 2%-Co doped ReS2 sample was highly efficient in both acid electrolyte (149 mV) and alkaline electrolyte (240 mV), achieving a current density of 10 mA cm−2 as well as superior long-term durability. [ABSTRACT FROM AUTHOR]

A series of boron carbon nitride–pyromellitic dianhydride (BCNPA) composites were successfully synthesized for the first time, where BCNPA3 exhibited the best adsorption and photodegradation performances for tetracycline (TC) under visible-light irradiation. 1H NMR characterization confirmed the fact that BCNPA3 was formed via the dehydration reaction between the OH groups in BCN and COOH groups in PA. Elemental N in BCNPA3 could capture protons and increase the pH of the TC solution from 3.73 to 6.80; consequently, TC changed from the positive state (pH 3.73) to the neutral state (pH 6.80). Subsequently, the adsorption capacity of BCNPA3 for TC increased from 66.24 mg g−1 (at pH 3.73) to 74.66 mg g−1 (at pH 6.80). This may be attributed to the fact that these captured protons can work as adsorption sites, too. Furthermore, the photodegradation efficiency of BCNPA3 for TC at pH 6.80 under visible-light irradiation was also higher than that at pH 3.73 (95% vs. 87%), because TC at pH 6.80 is less stable than that at pH 3.73. More interestingly, Cr(VI) could only be photoreduced into Cr(III) by BCNPA3 under visible-light irradiation when it coexisted with TC. This could be attributed to the fact that the photodegradation of TC increased the separation efficiency of the photoinduced electron and hole; consequently, the photoinduced electrons had sufficient time to reduce Cr(VI). Photoinduced ˙O2− and holes had the main contribution toward TC photodegradation by BCNPA3, while photoinduced electrons were responsible for Cr(VI) photoreduction. The adsorption and photodegradation performances of BCNPA3 for TC and Cr(VI) could be easily recovered under visible-light irradiation. [ABSTRACT FROM AUTHOR]

Considerable efforts have been directed towards constructing high-efficiency, earth-abundant and low-cost photocatalysts for hydrogen evolution under visible light irradiation. In this work, 2D ultrathin CoP-decorated bimetallic MnxCd1−xS photocatalysts were developed based on the combined strategies of controllable band structure and co-catalyst modification. An optimal H2 production rate of 65 324 μmol g−1 h−1 was obtained for the Mn0.5Cd0.5S/CoP-4% sample under visible light irradiation, which was 4.26 times higher than that of pure Mn0.5Cd0.5S as well as 38.7 times that of pure CdS. UV-vis and MS characterization results showed that the introduction of Mn into CdS could change the band potential towards a more negative direction, which would be beneficial for water reduction. Moreover, the added CoP could act as a co-catalyst to facilitate the electron transfer and restrain the recombination of photogenerated electron–hole pairs, which was testified by photocurrent, PL and EIS analyses. This work paves the way to offer a new direction towards designing efficient photocatalysts for hydrogen evolution. [ABSTRACT FROM AUTHOR]

Photocatalytic hydrogen evolution is a promising technology in solving the global energy and environment issues. Therefore, it is urgent to develop highly efficient, nonprecious metal and stable photocatalysts. In this work, we synthesized a highly efficient Ni2P–CdS/g-C3N4 composite based on the concept of combining heterojunction engineering with co-catalyst modification. When employed as a photocatalyst for water splitting, the obtained best composite (5% Ni2P–CdS/g-C3N4) displayed dramatically enhanced hydrogen evolution activity at the rate of 44 450 μmol h−1 g−1, which was about 27 times higher than that of pure CdS (1668 μmol h−1 g−1). The apparent quantum yield at 420 nm reaches 46.3%. The excellent photocatalytic activity and stability can be ascribed to the synergistic effect of the intimate contact between CdS and g-C3N4 and the surface co-catalyst modification. Specifically, the g-C3N4 coated on the CdS nanorods can effectively promote the electron−hole pair separation spatially and Ni2P can lower the overpotential of H+ reduction. [ABSTRACT FROM AUTHOR]

Wheat straw-derived biochar (BC-4-700) with a large surface area (2263.10 m2 g−1) has been synthesized using potassium hydroxide as an activating agent, and its sorption performance is evaluated by sorbing methylene blue (MB) and methyl orange (MO). The sorption behaviours of both MO and MB by BC-4-700 all follow pseudo-second-order and Langmuir models, and the driving forces for the two sorptions are attributed to the pi–pi interaction. The largest sorption quantity for MO by BC-4-700 is 3.24 mmol g−1, being 1.37 times larger than that for MB (2.36 mmol g−1). There is an inflection point in the isotherm sorption curve of MB. It is widely accepted that MB is a cationic dye and MO is an anionic dye. However, the two experimental phenomena cannot be explained well by the widely accepted MB+ form. The pH detection experiments on MB and MO solutions suggest that MO does not hydrolyze in water and the existing form in water is the well-accepted MO−, whereas MB hydrolyzes in water and the existing forms in water most likely include both the well-accepted MB+ and the hydrolyzed form of MB+. This finding can account well for the two experimental phenomena mentioned above, which is helpful to understand deeply the behaviour of organic cations in water and the sorption mechanism of organic cations by sorption materials. [ABSTRACT FROM AUTHOR]

In this study, BiOBr–titanium phosphate (BiOBr/TP) plate-on-plate composites with p–n heterojunctions were synthesized using a simple, feasible two-step method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and UV-vis diffuse reflectance spectrometry (DRS) were used to evaluate the structure, morphology and optical properties of the composites. Rhodamine B (RhB) and ciprofloxacin (CIP) were chosen as model pollutants to evaluate the photocatalytic activity of the synthesized samples under irradiation of both ultraviolet and visible light. The BiOBr/TP composites exhibited much higher photocatalytic activity for the degradation of both pollutants than pure TP. The enhanced photocatalytic performance can be ascribed to the formed p–n heterojunctions between p-type BiOBr and n-type TP, which efficiently reduced the recombination rate of photo-excited electrons and holes. Moreover, a possible photocatalytic mechanism of organic pollutant degradation by the obtained samples was presented in detail. [ABSTRACT FROM AUTHOR]

In this paper, novel p–n type heterojunction BiOI/La2Ti2O7 nanocomposites were synthesized via a simple method for obtaining visible light activated photocatalysts. The crystal phases and crystallinity of the prepared samples were analyzed by X-ray diffraction (XRD). The morphologies of the BiOI/La2Ti2O7 composites were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The elemental composition and states were analyzed by X-ray photoelectron spectroscopy (XPS). Results showed that the obtained composites were constructed by 2D BiOI and La2Ti2O7 nanosheets. Besides, UV-vis diffuse reflectance spectrometry (DRS) indicated that BiOI/La2Ti2O7 composites possessed better visible light absorptive properties than pure La2Ti2O7. The photocatalytic activity was evaluated by the degradation of Rhodamine B (RhB), dye X-3B, methyl orange (MO) and a colorless antibiotic agent, ciprofloxacin (CIP), under visible light irradiation. Results showed that BiOI/La2Ti2O7 composites exhibited much higher activity than the corresponding single components. First of all, the enhanced activity can be ascribed to the improved visible light harvesting. Secondly, the results of photo-induced current and photoluminescence spectroscopy illustrated that the enhanced performance can also be attributed to the efficient transfer and separation of photoinduced charges, which resulted from the formed p–n heterojunctions between BiOI and La2Ti2O7. It can be expected that this novel 2D–2D p–n heterostructured photocatalyst would be a promising candidate for environmental remediation. [ABSTRACT FROM AUTHOR]

Hydrogen evolution by photocatalytic water splitting has attracted extensive attention in recent years. Here we report a composite photocatalyst, in which graphene and Pt particles act as cocatalysts to modify CdS nanowires. This composite photocatalyst was prepared by a solvothermal method followed by a photoreduction process. The obtained samples were characterized by X-ray powder diffraction, UV-vis diffuse reflectance spectroscopy, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, photoluminescence and Brunauer–Emmett–Teller specific surface area analysis. The graphene and Pt comodified CdS nanowires gain a high hydrogen evolution rate of 3984 μmol h−1 g−1, which is almost 4 times higher than that of bare CdS nanowires and also higher than the sum of graphene–CdS and Pt–CdS nanowires. The obtained sample also exhibits a good stability. The encouraging results presented here can be attributed to the incorporation of graphene and Pt which show a synergetic effect for hydrogen evolution. This work paves a way to the potential application of CdS nanowires in energy conversion. [ABSTRACT FROM AUTHOR]

In this work, a series of novel flower-like Bi2O2CO3/CdS heterojunctions were prepared by a simple and feasible two-step process. The phase structures of as-prepared samples were examined by X-ray diffraction (XRD). Scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were used to confirm the flower-like heterostructures of the Bi2O2CO3/CdS composites. The Brunauer–Emmett–Teller (BET) specific surface area (SBET) of samples were analyzed by N2 adsorption–desorption isotherms. UV-vis diffuse reflectance spectrometry (DRS) revealed that Bi2O2CO3/CdS heterojunctions exhibited better light absorptive properties than pure Bi2O2CO3. The photocatalytic activity was investigated by the degradation of MB under visible light irradiation. The results showed that the as-prepared Bi2O2CO3/CdS heterojunctions exhibited much higher activity than pure Bi2O2CO3. The photoluminescence (PL) spectra and photocurrent studies indicated that the recombination of photogenerated electron–hole pairs was decreased effectively due to the formation of heterojunctions between flower-like Bi2O2CO3 and CdS nanoparticles. Trapping experiments indicated that ṖO2− radicals were the main reactive species for MB degradation in the present photocatalytic system. Furthermore, the cycling experiments revealed the good stability of Bi2O2CO3–CdS composites. [ABSTRACT FROM AUTHOR]

Simultaneous measurements of dissolved iron (Fe), phosphorus (P), and arsenic (As) were made using the diffusive gradients in thin films technique equipped with a mixed binding gel impregnated with zirconium oxide and Chelex-100 (ZrO–Chelex DGT). The ZrO–Chelex binding gel exhibited rapid binding dynamics to Fe(ii), P(PO43−), and As(iii)/As(v) in mixed solutions of the three elements. The bound Fe, P, and As could be quantitatively recovered using an established four-step elution procedure. Simultaneous measurements of the three elements with ZrO–Chelex DGT were validated through time-series experiments, and there was no influence of pH (4.1 to 7.1) and ionic strength (0.01 to 800 mM). The DGT capacities for As(iii) and As(v) were 69.0 μg and 186 μg per device, respectively, which were much greater than those of the widely used ferrihydrite DGT. Applications in synthesized freshwaters and in sediments further confirmed its feasibility in simultaneous measurements in the environment. The present study offered that the ZrO–Chelex DGT will be a useful tool in in situ monitoring of Fe–P–As and assessment of their interactions in the biogeochemical processes. [ABSTRACT FROM AUTHOR]

Ag/AgCl@chiral TiO2 nanofibers are synthesized to tune the angle of the incident visible light through the chiral structure of the TiO2 nanofibers, intensifying the surface plasmon resonance effect of the supported Ag/AgCl materials, which are proven to be a highly active and stable visible light photocatalyst for the degradation of 17-β-ethinylestradiol. [ABSTRACT FROM AUTHOR]

Surface acid site regulation of photocatalysts is a promising strategy to improve their performance. Herein, surface acid sites of cadmium sulfide were rationally regulated by cerium doping, which resulted in significantly increased photocatalytic activity for tetracycline hydrochloride (TC-HCl) degradation. The generated Brønsted acid sites were verified to favor the adsorption of organic molecules because of their strong affinity. Meanwhile, Lewis acid sites acted as the active sites for C-C bond cleavage via a nucleophilic substitution process, which was testified by the Fukui function and electrostatic potential. Besides, Ce 3+ doping suppressed the recombination of electron-hole pairs, which also boosted the performance of TC-HCl degradation. Moreover, the degradation pathway of TC-HCl was deduced based on theoretical calculations and HPLC-MS results. The toxicity of pollutants and intermediates was also evaluated. This work provided new insight into the rational design and preparation of highly efficient photocatalysts for environmental purification.

Cobalt-modified rhenium disulfide nanosheets rich in defects, obtained by following an ingenious atom substitution strategy, exhibited boosted HER performance. The 2%-Co doped ReS2 sample was highly efficient in both acid electrolyte (149 mV) and alkaline electrolyte (240 mV), achieving a current density of 10 mA cm-2 as well as superior long-term durability.

Considerable efforts have been directed towards constructing high-efficiency, earth-abundant and low-cost photocatalysts for hydrogen evolution under visible light irradiation. In this work, 2D ultrathin CoP-decorated bimetallic MnxCd1-xS photocatalysts were developed based on the combined strategies of controllable band structure and co-catalyst modification. An optimal H2 production rate of 65 324 μmol g-1 h-1 was obtained for the Mn0.5Cd0.5S/CoP-4% sample under visible light irradiation, which was 4.26 times higher than that of pure Mn0.5Cd0.5S as well as 38.7 times that of pure CdS. UV-vis and MS characterization results showed that the introduction of Mn into CdS could change the band potential towards a more negative direction, which would be beneficial for water reduction. Moreover, the added CoP could act as a co-catalyst to facilitate the electron transfer and restrain the recombination of photogenerated electron-hole pairs, which was testified by photocurrent, PL and EIS analyses. This work paves the way to offer a new direction towards designing efficient photocatalysts for hydrogen evolution.

In this study, BiOBr-titanium phosphate (BiOBr/TP) plate-on-plate composites with p-n heterojunctions were synthesized using a simple, feasible two-step method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and UV-vis diffuse reflectance spectrometry (DRS) were used to evaluate the structure, morphology and optical properties of the composites. Rhodamine B (RhB) and ciprofloxacin (CIP) were chosen as model pollutants to evaluate the photocatalytic activity of the synthesized samples under irradiation of both ultraviolet and visible light. The BiOBr/TP composites exhibited much higher photocatalytic activity for the degradation of both pollutants than pure TP. The enhanced photocatalytic performance can be ascribed to the formed p-n heterojunctions between p-type BiOBr and n-type TP, which efficiently reduced the recombination rate of photo-excited electrons and holes. Moreover, a possible photocatalytic mechanism of organic pollutant degradation by the obtained samples was presented in detail.

In this paper, novel p-n type heterojunction BiOI/La2Ti2O7 nanocomposites were synthesized via a simple method for obtaining visible light activated photocatalysts. The crystal phases and crystallinity of the prepared samples were analyzed by X-ray diffraction (XRD). The morphologies of the BiOI/La2Ti2O7 composites were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The elemental composition and states were analyzed by X-ray photoelectron spectroscopy (XPS). Results showed that the obtained composites were constructed by 2D BiOI and La2Ti2O7 nanosheets. Besides, UV-vis diffuse reflectance spectrometry (DRS) indicated that BiOI/La2Ti2O7 composites possessed better visible light absorptive properties than pure La2Ti2O7. The photocatalytic activity was evaluated by the degradation of Rhodamine B (RhB), dye X-3B, methyl orange (MO) and a colorless antibiotic agent, ciprofloxacin (CIP), under visible light irradiation. Results showed that BiOI/La2Ti2O7 composites exhibited much higher activity than the corresponding single components. First of all, the enhanced activity can be ascribed to the improved visible light harvesting. Secondly, the results of photo-induced current and photoluminescence spectroscopy illustrated that the enhanced performance can also be attributed to the efficient transfer and separation of photoinduced charges, which resulted from the formed p-n heterojunctions between BiOI and La2Ti2O7. It can be expected that this novel 2D-2D p-n heterostructured photocatalyst would be a promising candidate for environmental remediation.

In this work, a series of novel flower-like Bi2O2CO3/CdS heterojunctions were prepared by a simple and feasible two-step process. The phase structures of as-prepared samples were examined by X-ray diffraction (XRD). Scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were used to confirm the flower-like heterostructures of the Bi2O2CO3/CdS composites. The Brunauer-Emmett-Teller (BET) specific surface area (SBET) of samples were analyzed by N2 adsorption-desorption isotherms. UV-vis diffuse reflectance spectrometry (DRS) revealed that Bi2O2CO3/CdS heterojunctions exhibited better light absorptive properties than pure Bi2O2CO3. The photocatalytic activity was investigated by the degradation of MB under visible light irradiation. The results showed that the as-prepared Bi2O2CO3/CdS heterojunctions exhibited much higher activity than pure Bi2O2CO3. The photoluminescence (PL) spectra and photocurrent studies indicated that the recombination of photogenerated electron-hole pairs was decreased effectively due to the formation of heterojunctions between flower-like Bi2O2CO3 and CdS nanoparticles. Trapping experiments indicated that ˙O(2-) radicals were the main reactive species for MB degradation in the present photocatalytic system. Furthermore, the cycling experiments revealed the good stability of Bi2O2CO3-CdS composites.

Ag/AgCl@chiral TiO2 nanofibers are synthesized to tune the angle of the incident visible light through the chiral structure of the TiO2 nanofibers, intensifying the surface plasmon resonance effect of the supported Ag/AgCl materials, which are proven to be a highly active and stable visible light photocatalyst for the degradation of 17-β-ethinylestradiol.