Latest ArticlesThe rapid recombination of photoinduced electron-hole pairs as well as the deficiency of high-energy carriers restricted the redox ability and products selectivity. Herein, the heterojunction of SnS2-decorated three-dimensional ordered macropores (3DOM)-SrTiO3 catalysts were in-situ constructed to provide transmit channel for high-energy electron transmission. The suitable band edges of SnS2 and SrTiO3 contribute to the Z-scheme transfer of photogenerated carrier. The 3DOM structure of SrTiO3-based catalyst possesses the slow light effect for enhancing light adsorption efficiency, and the surface alkalis strontium is benefit to the boosting adsorption for CO2. The in-situ introduced SnS2 decorated on the macroporous wall surface of 3DOM-SrTiO3 altered the primary product from CO to CH4. The Z-scheme electron transfer from SnS2 combining with the holes in SrTiO3 occurred under full spectrum photoexcitation, which improved the excitation and utilization of photogenerated electrons for CO2 multi-electrons reduction. As a result, (SnS2)3/3DOM-SrTiO3 catalyst exhibits higher activity for photocatalytic CO2 reduction to CH4 compared with single SnS2 or 3DOM-SrTiO3, i.e., its yield and selectivity of CH4 are 12.5 μmol g-1 h-1 and 74.9%, respectively. The present work proposed the theoretical foundation of Z-scheme heterojunction construction for enhancing photocatalytic activity and selectivity for CO2 conversion.
At present, the assessment of photooxidation system mainly focuses on the photodegradation efficiency of target pollutant, lacking of the toxicity assessment in the photocatalysis process. Here, photodecomposition of bisphenol A (BPA) was used to investigate the performance of several cyclodextrin modified photocatalysts. Moreover, the comprehensive toxicity changes of BPA under different photocatalytic oxidation conditions were conducted. The β-cyclodextrin (β-CD) modified photocatalyst, including titanium dioxide (CM-β-CD-TiO2), carbon nitride (CM-β-CD-C3N4) and cadmium sulfide (SH-β-CD-AM/CdS) exhibit high degradation rate and mineralization efficiency of BPA. The highest total organic carbon (TOC) removal of BPA observed in the oxidation system of SH-β-CD-AM/CdS nanoreactor (73.4%). The main oxidation intermediates in these systems were detected, and the comprehension toxicity of BPA and its oxidation intermediates in different system were compared by toxicity estimation software tool (T.E.S.T.) based on quantitative structure-activity relationship (QSAR) prediction. The results show that β-CD can facilitate the photodecomposition of the target contaminant. However, many oxidation intermediates with high comprehensive toxicity, even in the oxidation system with high BPA removal, can still be detected. Therefore, not only decomposition of target contaminant but also the comprehensive toxicity of oxidation intermediates should be regarded as index to evaluate a photocatalysis technology.
Graphitic carbon nitride (g-C3N4)-based materials are regarded as one of the most potential photocatalysts for utilizing solar energy. In this work, we reported a facile one step in-situ hydrothermal-roasting method for preparing honeycomb-like g-C3N4/CeO2 nanosheets with abundant oxygen vacancies (g-C3N4/CeO2-x). The hydrothermal-roasting and incomplete-sealed state can (ⅰ) generate an in-situ reducing atmosphere (CO, N2, NH3) to tune the concentration of oxygen vacancies in CeO2; (ⅱ) beneficial to prevent continuous growth of g-C3N4 and results in honeycomb-like g-C3N4/CeO2-x hybrid nanosheets. What is more, the g-C3N4/CeO2-x photocatalyst exhibited extended photoresponse range, increased specific surface area and obviously enhanced separation efficiency of photogenerated electron-hole pairs. As a proof-of-concept application, the optimized g-C3N4/CeO2-x nanosheets could achieve 98% removal efficiency for Cr(Ⅵ) under visible light irradiation (λ ≥ 420 nm) within 2.5 h, which is significantly better than those of pure g-C3N4 and CeO2. This work provides a new idea for more rationally designing and constructing g-C3N4-based catalysts for efficient extended photochemical application.
Composting can enhance the nutrient elements cycling and reduce carbon dioxide production. However, little information is available regarding the application of compost for the remediation of the contaminated soil. In this study, we assess the response of the redox capacities (electron accepting capacities (EAC) and electron donating capacities (EDC)) of compost-derived humic acids (HAs) to the bioreduction of hexavalent chromium (Cr(VI)), especially in presence of hematite. The result showed that the compost-derived HAs played an important role in the bioreduction of Cr(VI) in presence and absence of hematite under the anoxic, neutral (pH 7) and motionless conditions. Based on the pseudo-first order kinetic model, the rate constants of Cr(VI) reduction increased by 1.36–2.0 times when compost-derived HAs was added. The redox capacity originating from the polysaccharide structure of compost-derived HAs made them effective in the direct Cr(VI) reduction (without MR-1) at pH 7. Meanwhile, the reduction rates were inversely proportional to the composting treatment time. When iron mineral (Fe2O3) and compost-derived HAs were both present, the rate constants of Cr(VI) reduction increased by 2.35–5.09, which were higher than the rate of Cr(VI) reduction in HA-only systems, indicating that the hematite played a crucial role in the bioreduction process of Cr(VI). EAC and quinonoid structures played a major role in enhancing the bioreduction of Cr(VI) when iron mineral and compost-derived HAs coexisted in the system. The results can extend the application fields of compost and will provide a new insight for the remediation of Cr(VI)-contaminated soil.
The development in technology of synthetic azo dyes, has led to excessive water resources pollution. Even at lower concentration they can impart the quality of water and human life. Herein, we have developed a novel synthesis strategy via introducing salicylic acid (SA) for the synthesis of a leachy crystalline material H-MIL-53(Fe) with hierarchical pores (HP) and exposed coordination unsaturated sites (CUS), which had higher surface area and larger pore volume than the as synthesized MIL-53(Fe). Due to these characteristics, H-MIL-53(Fe) was competent removal of orange G (OG, one of the frequently used azo dyes) with equilibrium in 300 min and the maximum adsorption capacity of 163.9 mg/g. The adsorption mechanism of OG onto H-MIL-53(Fe) was mostly based on electrostatic attraction between CUS of H-MIL-53(Fe) along with HP as active species to OG diffusion and bind. By comparing H-MIL-53(Fe) with other adsorbents for OG adsorption, it is undoubtedly that H-MIL-53(Fe) can be used as a promising adsorbent for OG removal from aqueous solutions.
Hydrogenation of CO2 to value-added chemicals has attracted much attention all through the world. In2O3 with cubic bixbyite-type (denoted as c-In2O3) is well known for its high CO2 hydrogenation activity and CH3OH selectivity at high temperature. However, the other structure of In2O3 with rhombohedral corundum-type (denoted as rh-In2O3) rarely been investigated as catalyst. Herein, c-In2O3 and rh-In2O3 were prepared and comparatively studied for CO2 hydrogenation. The results indicated that c-In2O3 showed higher CO2 conversion activity than rh-In2O3 due to the impressive reducibility and reactivity. Whereas rh-In2O3 had higher CH3OH selectivity due to weaker CH3OH and stronger CO adsorption on rh-In2O3. Although c-In2O3 and rh-In2O3 catalysts showed different CO2 hydrogenation performance, in-situ diffuse reflectance infrared Fourier transform spectroscopy showed CO2 can be reduced to CO through redox cycling and hydrogenation to CH3OH through formate path.
Photocatalyst is the most widespread method in advanced oxidation technologies, but due to the photo-induced electron combine easily with hole and the wavelength of adsorption is limited which will affect some practical applications. Carbon quantum dots (CQDs) is non-toxic and harmless green materials, it has the ability to improve the photocatalytic effect which is attributed to its good electrical and optical properties. Their up-conversion effect, photosensitization and electrical conductivity are assistants which help promote the photocatalytic effect in environmental applications. The key mechanisms of CQDs to improve photocatalysis can be roughly divided into three categories: 1) Up-conversion effect converts the incident light into the emitted light with high energy to solve the problem which is the light absorption range; 2) CQDs act as a photosensitizer instead of valence band to provide electrons to the conduction band of semiconductor; 3) CQDs can be used as the internal or external electronic conductor in materials to alleviate the trend of electron and hole separation. However, CQDs and CQDs-based photocatalysts have different views to solve environmental problems, so it is necessary to integrate different views. Therefore, this review is mainly aimed at the recent researches about the preparation processes of CQD, CQDs-based photocatalysts, and their ability to remove environmental pollutants, with a special emphasis on the mechanism for depredating pollutants. Furthermore, this paper analyzes and discusses the prospects and challenges of CQDs in the environmental field.
Graphene oxide (GO) membranes show great potential in molecular separation for water treatment. However, the inferior stability of GO membranes is a major bottleneck for practical applications. In this study, bio-inspired polydopamine (PDA) deposition is reported for enhancing the stability of GO membranes. Through simple and mild immersion, PDA is self-polymerized on GO membranes. The blocking of PDA chains to membrane defects improves the rejections for various molecules. Because the inherently strong adhesion and crosslinking of PDA greatly strengthen the interactions of substrates to GO layers and the binding force of GO nanosheets, the prepared PDA-GO membranes exhibit impressive long-term stability in cross-flow filtration, and maintain good nanofiltration performance at various feed pressures, tangential velocities, and even after external scratching. Moreover, because the deposited PDA layers obstruct the direct contact between GO and contaminants, the antifouling property of the PDA-GO membranes increases substantially, with recovery ratio about 98%.
This study aimed to construct a photoelectrocatalytic (PEC) reaction system based on the self-made reduced TiO2 NTAs (r-TNAs) photoanode and activated carbon/Polytetrafluoroethylene (AC/PTFE) cathode. It would be observed clearly that the degradation rate constant of carbamazepine (CBZ) over r-TNAs(photoanode)-AC/PTFE(cathode) PEC system (0.04961 min-1) was even higher than that of r-TNAs(photoanode)-Pt(cathode) PEC system (0.04602 min-1) with the assistance of visible light irradiation and +0.4 V external potential. Besides, in order to obtain optimized conditions, the influence of key parameters such as pH value, electric current density and electrolyte concentration were studied. Most importantly, photoelectrochemical (PECH) properties, reactive oxide species contribution, ·OH formation rate and CBZ degradation pathway were determined. The results illustrated that the excellent PEC degradation performance depended on the excellent photocatalytic property of r-TNAs photoanode and electron transfer property of photoelectrodes in r-TNAs(photoanode)-AC/PTFE(cathode) PEC system. Therefore, the study demonstrated that the r-TNAs(photoanode)-AC/PTFE(cathode) PEC system could be expected to replace metal-catalyzed cathodes depending on its excellent PEC performance activity and low cost as well as the reaction system possessed objective and practical application prospect.
The removal efficiency of pollutants in Fe(0) electrocoagulation (EC) has been associated closely with the speciation of generated Fe(II)/Fe(III) oxides during this process, which is very complicated and can be affected by various factors. In this work, in-situ Raman, X-ray diffraction and some other techniques have been used to study the speciation of Fe under different conditions and to establish a relationship between Fe speciation and Sb(V) removal efficiency. Results indicated that concentration of dissolved oxygen (DO) is a key factor influencing Fe(0) EC. It was found that green rusts (GRs) were formed and were then transformed into magnetite at lower DO concentration, and Sb(V) removal efficiency reached 99.9% after 30 min of EC. In contrast, γ-FeOOH was formed at high DO concentration, and the removal efficiency of Sb(V) after 30 min of EC was only 72.8%. In the presence of sulfite and phosphate with low concentrations, GRs can be stabilized and benefit the removal of Sb(V). We believe this work will provide some new insights on the mechanism of Fe(0) EC and the effective removal of other pollutants during Fe(0) EC process.
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