Latest ArticlesLargely limited by the high dissociation energy of the O—O bond, the photocatalytic molecular oxygen activation is highly challenged, which restrains the application of photocatalytic oxidation technology for atmospheric pollutants removal. Herein, we design and fabricate the InP QDs/g-C3N4 compounds. The introduction of InP QDs promotes the charge transfer within the interface resulting in the effective separation of photo-generated carriers. Furthermore, InP QDs greatly facilitates the activation of molecular oxygen and promote the formation of O2·- under visible-light illumination. These conclusions are identified by experimental and calculation results. Hence, NO can be combined with the O2·- to form O—O—N—O intermediate to direct conversion into NO3-. As a result, the NO removal ratio of g-C3N4 has a onefold increase after InP QDs loaded and the generation of NO2 is effectively inhibited. This work may provide a strategy to design highly efficient materials for molecular oxygen activation.
From emerging pollutants to emerged threat, researchers are continuously looking for promising technologies for wastewater treatment. Adsorption has been identified as the most convenient approach for treating wastewater at low-cost and with high-efficiency. Recently, graphene and its derivatives have gained heightened attention as novel adsorbents because of their unique molecular structure and outstanding physicochemical properties. Heavy metals, dyes, polycyclic aromatic hydrocarbons (PAHs) and other pollutants, which are widely concerned recently, all show different adsorption behaviors. Numerous functional groups, resonating and delocalized π-electron system of graphene derivatives lead to the formation of various adsorptive interactions i.e., π-π interactions, electrostatic interactions, H-bonding, etc. with these venomous pollutants, and quarantine them in solution. The pristine form of graphene subsidiaries tends to exhibit low sorption efficiency due to high propensity of agglomeration, lack of selectivity, hydrophobicity and difficulty in phase separation after treatment. Therefore, designing of efficient graphene composites through the surface modification with numerous functional groups, polymers or nanoparticles is an ongoing challenge. Complex graphene composites are increasingly reported, but the fate of pollutants and adsorption mechanisms are still far to be fully clarified. This review summarizes the recent progresses in the application of graphene-based adsorbents for eliminating a wide range of organic and inorganic pollutants from wastewater. A critical explanation is provided on the synthesis of graphene adsorbents, systematic adsorption and desorption mechanisms along with their pollutant removal performances under different experimental conditions. A brief perspective on upcoming research needs and challenges involved in the designing of high-quality graphene-based adsorbents are highlighted.
In this study, a carbon quantum dots modified maghemite catalyst (CQDs@γ-Fe2O3) has been synthesized by a one-step solvothermal method for efficient persulfate (PDS) activation under visible light irradiation. Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) characterization indicated that the formation of heterojunction structure between CQDs and γ-Fe2O3 effectively reduced the catalyst band gap (Eg), favoring the separation rate of electrons and holes, leading to remarkable efficient sulfamethoxazole (SMX) degradation as compared to the dark-CQDs@γ-Fe2O3/PDS and vis-γ-Fe2O3/PDS systems. The evolution of dissolved irons also demonstrated that CQDs could accelerate the in-situ reduction of surface-bounded Fe3+. Electron paramagnetic resonance (EPR) and radical scavenging experiments demonstrated that both ·OH and SO4·- were generated in the reaction system, while ·OH was relatively more dominant than SO4·- for SMX degradation. Finally, the reaction mechanism in the vis-CQDs@γ-Fe2O3/PDS system was proposed involving an effective and accelerated heterogeneous-homogeneous iron cycle. CQDs would enrich the photo-generated electrons from γ-Fe2O3, causing efficient interfacial generation of surface-bond Fe2+ and reduction of adsorbed Fe3+. This visible light induced iron cycle would eventually lead to effective activation of PDS as well as the efficient degradation of SMX.
Metal organic frameworks (MOFs) has broad application prospect in separation, catalysis, and adsorption. By a facile green method, we successfully fabricated prGO@cHKUST-1 composite membrane with the modification of dopamine and orientated growth of MOFs. Mg/Al-layered double hydroxides (Mg/Al-LDHs) was used as a modulator to obtain cubic HKUST-1 (cHKUST-1) with excellent morphology and special properties. Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) etc. characterization illustrated successful synthesis of cHKUST-1 and composite membranes. Cubic HKUST-1 can tune the inter-layer spacing of graphene oxide (GO) leading increase in hydrophilicity and flux of the membrane. Meanwhile, the reduction effect of PDA and intercalation effect of MOFs could change the stacked way of GO layers, forming several fuzzy pores and more active sites on membrane surface. The prGO@cHKUST-1 membrane has an excellent rejection for methylene blue (MB) (99.5%) and Congo red (CR) (71.2%). Moreover, the modified membrane exhibited 10 and 5 times higher permeation flux than that of original GO membrane and prGO membrane, respectively. Thus, using orientated growth of MOFs to synthesize GO based composite membrane will provide useful insights in ultrahigh permeation flux membranes of dye and oil-water emulsion separation.
The contamination of antibiotics in aqueous environment causes increasing concerns recently. Light-assisted activation of peroxydisulfate (PDS) has been demonstrated as an efficient technology for removal of contamination in water. Herein, a hollow sphere of CuWO4 (h-CuWO4) was employed as a visible light-activated photocatalyst for the activation of PDS, and following with high removal efficiency (98%) of antibiotic sulfamethoxazole (SMX). Under visible light irradiation, the degradation rate on hollow structures system is nearly 2 times higher than the traditional solid CuWO4 spheres. Furthermore, the underlying mechanism and detailed pathway of SMX degradation were proposed based on density functional theory (DFT) calculations and liquid chromatography-mass spectrometry (LC–MS). This work provides a new feasible way for advanced oxidation processes to remove antibiotics SMX in heterogeneous system, and open up new application possibilities of CuWO4-based materials.
In this work, the reduction of mercury ions (Hg2+) to elemental mercury (Hg0) was easily achieved using highly reductive carbon dots (r-CDs), which synthesized from sucrose by a simple and cost-effective method. After a careful mechanistic study, the reduction was probably accomplished with the large numbers of electrons contained in r-CDs rather than the oxidation of its functional groups. Additionally, a 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay showed that the r-CDs were nontoxic to wildlife and human beings. Consequently, the r-CDs were used as an alternative to toxic reductants (SnCl2 or NaBH4) for the sensitive and in situ determination of mercury by cold vapor generation (CVG) coupled to a miniature point discharge optical emission spectrometer (μPD-OES). Limit of detection of 0.05 μg/L was obtained for Hg2+, with relative standard deviation (RSD) less than 5.4% at a concentration of 5 μg/L. The accuracy of r-CDs induced CVG-μPD-OES was validated by the determination of mercury in a certified reference material (DOLT-5, dogfish liver) and five natural water samples collected from different rivers and lakes in Chengdu City. Since r-CDs are nontoxic and prepared from abundant and inexpensive sucrose, the r-CDs induced CVG-μPD-OES retains the great potential for the inexpensive and environmentally friendly field analysis of mercury in natural water. The accuracy of the proposed method was validated by the analysis of a certified reference material and several water samples with satisfactory results.
The heterogeneous reaction of SO2 on mineral dust surfaces is generally considered as an important chemical pathway for secondary sulfate formation in the troposphere. To this day, there are no reported studies that assess the impact of atmospheric CO2 in sulfate production on mineral dust surfaces. In this work, we investigate the impact of CO2 on SO2 uptake on dust proxy aluminum oxide particles using a diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). CO2 is demonstrated to suppress the heterogeneous oxidation of SO2 on alpha-Al2O3. Compared to that measured in the CO2-free case, the uptake coefficient is decreased by nearly 57% when Al2O3 particles are exposed to the gas flow with atmospheric CO2 at a relative humidity (RH) of 25%. It is also found that there is a balance between the yield of active moiety —OH provided by Al(OH)3(CO)(OH)2 clusters and the loss of basic hydroxyl group on aluminum oxide surfaces blocked by CO2-derived (bi)carbonate species. This work, for the first time, reveals a negative effect of atmospheric CO2 on the sulfate formation, which potentially decreases solar-radiation scattering and further exacerbates global warming.
The high cost and low reserves of noble metals greatly hinder their practical applications in new energy production and conversion. The exploration of cost-effective alternative electrocatalysts with the ability to drive hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is extremely significant to promote overall water splitting. Herein, ultrathin CoSe2/CNTs nanocomposites have been synthesized by a facile two-step method, where the ultrathin Co-MOF (metal organic-framework) decorated with cable-like carbon nanotubes (CNTs) (Co-MOF/CNTs) was initially fabricated, and followed a low-temperature selenization process. The ultrathin CoSe2 nanosheets as well as the superior conductivity of CNTs synergistically resulted in abundant active sites and enhanced conductivity to boost the electrocatalytic activity. The as-prepared CoSe2/CNTs electrocatalysts exhibited an overpotential of 190 mV and 300 mV vs. reversible hydrogen electrode (RHE) at a current density of 10 mA/cm2 for the HER and OER in alkaline solution, respectively, and demonstrated superior durability. Furthermore, the as-prepared bifunctional CoSe2/CNTs electrocatalysts can act as cathode and anode in an electrolyzer, showing a cell voltage of 1.75 V at 10 mA/cm2 for overall water splitting.
Heavy metal complexes with high mobility are widely distributed in wastewater from modern industries, which are more stable and refractory than free heavy metal ions. Their removals from wastewater draw increasing attentions and various technologies have been developed, among which advanced oxidation processes (AOPs) are more effectively and promising. Progresses on five representative types of AOPs, including Fenton (like) oxidation, electrochemical oxidation, photocatalytic oxidation, ozonation and discharge plasma oxidation for heavy metal complexes degradation are summarized in this review. Their rationales, advantages, applications, challenges and prospects are introduced independently. Combi-nations among these AOPs, such as electrochemical Fenton oxidation and photoelectrocatalytic oxidation, are also comprehensively highlighted. Future efforts should be made to reduce acid requirement and scale up for practical applications of AOPs for heavy metal complex degradation efficiently and cost-effectively.
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.
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