Latest ArticlesThis study evaluated the removal of multiple pollutants, i.e., polybrominated diphenyl ethers (PBDEs), novel halogenated flame retardants (HFRs), sulfonamide antibiotics (SAs), and heavy metals (HMs), by a full-scale reversed A2/O process in a sewage treatment plant (STP) in Guangzhou, China. The reversed A2/O process demonstrated high removal efficiencies (REs) for total PBDEs (60.5%±4.3%), novel HFRs (98.4%±2.8%) and HMs (70.1%±1.2%), and a relatively low RE for SAs (25.0%±2.3%). BDE 209, the dominant PBDE congener, showed a high residual concentration (13.41±5.18 ng/L) in the suspended particulate matter (SPM) of treated effluents. Some novel HFRs, dechlorane plus (DP) and decabromodiphenyl ethane (DBDPE), were detected in the SPM of the raw sewage (7.50±4.14 ng/L and 11.52±11.65 ng/L, respectively). The removal of SAs was mainly through biodegradation in the activated sludge bioreactors(ASBs).Of the HMs, Mn and Ni exhibited the lowest REs (47.5%±2.2% and 35.0%±2.6%, respectively), while Cr and Cu showed the highest removal (REs > 80%). In terms of treatment units in the reversed A2/O process, ASBs showed the highest RE (27.8%) for the multiple pollutants. The information can aid in our understanding of removal properties of STPs on various pollutants and evaluating the ecological/health risks of STPs as point pollutant sources.
Algae are potential feedstock for the production of bioenergy and valuable chemicals. After the extraction of specific value-added products, algal residues can be further converted into biogas, biofuel, and biochar through various thermochemical treatments such as conventional pyrolysis, microwave pyrolysis, hydrothermal conversion, and torrefaction. The compositions and physicochemical characteristics of algal biochar that determine the subsequent applications are comprehensively discussed. Algal biochar carbonized at high-temperature showed remarkable performance for use as supercapacitors, CO2 adsorbents, and persulfate activation, due to its graphitic carbon structure, high electron transport, and specific surface area. The algal biochar produced by pyrolysis at moderate-temperature exhibits high performance for adsorption of pollutants due to combination of miscellaneous functional groups and porous structures, whereas coal fuel can be obtained from algae via torrefaction by pyrolysis at relatively low-temperature. The aim of this review is to study the production of algal biochar in a cost-effective and environmental-friendly method and to reduce the environmental pollution associated with bioenergy generation, achieving zero emission energy production.
Largely 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.
Sulfur-driven autotrophic denitrification (SDAD), a process suited for the treatment of nitrogen and sulfur-polluted wastewater without extra supplement of organic carbon, is a promising biological nitrogen removal process. However, the SDAD process was affected by many factors such as various electron donors, organic carbon and exogenous substances (e.g., antibiotics and heavy metal), which prevent further application. Thus, we conducted a detailed review of previous studies on such influence factors and its current application. Besides, a comparative analysis was adopted to recognize the current challenges and future needs for feasible application, so as to ultimately perfect the SDAD process and extend its application scope.
The selective catalytic reduction (SCR) of NOx by NH3 is one of the most mature technologies for NOx treatment. Catalysts are the main factors affecting denitrification efficiency. Zeolites as low-temperature NH3-SCR catalysts have been extensively studied in the past few years. In this work, the mechanism of zeolites for NH3-SCR reaction was reviewed and the denitrification performances of zeolite catalysts prepared by different methods were compared. The effects of sulfur and water poisoning on zeolite catalysts in NH3-SCR reaction were also analyzed. Several ways to address the problems in low-temperature NH3-SCR reaction were discussed. Hopefully, this review could provide a fundamental understanding of SCR reaction on zeolite catalysts and pave the way toward similar studies to realize its commercial applications.
The binary Ag3PO4/MIL-125-NH2 (AMN-X) composites were synthesized through ion exchange-solution method, and the ternary Ag/Ag3PO4/MIL-125-NH2 (AAMN-X) Z-scheme heterojunctions were prepared via the photo chemical reduction deposition strategy. The photocatalytic hexavalent chromium (Cr(Ⅵ)) sequestration over AMN-X and AAMN-X were investigated under visible light. AAMN-120 accomplished superior reduction performance due to that Ag nanoparticles (NPs) act as electrons transfer bridge to enhance the separation efficiency of photogenerated e--h+ pairs, in which the reaction rates (k value) were 2.77 and 124.2 fold higher than those of individual MIL-125-NH2 and Ag3PO4, respectively. The influences of different pH values, small organic acids and coexisting ions on the photocatalytic performance of AAMN-120 were also investigated. In addition, the AAMN-120 heterojunction expressed great reusability and stability in cycling experiments. The mechanism of photocatalytic Cr(Ⅵ) was investigated and verified through photoluminescence (PL), electrochemistry, electron spin resonance (ESR), active species capture, and Pt element deposition experiments.
Efficient generation of singlet oxygen (1O2) by an excitonic energy transfer process is highly desired on a semiconductor photocatalyst for selective oxidation of methyl phenyl sulfide (MPS). Herein, it is demonstrated that a large amount of 1O2 is produced on pristine graphitic carbon nitride (CN) nanosheet compared with bismuth oxybromide (BiOBr) and commercial P25 titanium dioxide (TiO2). This leads to a certain photoactivity of CN for MPS oxidation. The observed ~77% selectivity for CN depends on the competitive results of excitonic energy transfer for 1O2 formation and charge carrier separation for superoxide radical (O2·-) production, which are based on the phosphorescence spectra and electron paramagnetic resonance signals, respectively. Moreover, ultrathin CN nanosheets are synthesized by thermal treatment with the cyanuric acid-melamine hydrogen bonded aggregates as precursors. It is confirmed that the amount of produced 1O2 could be increased by decreasing the thickness of resultant CN nanosheets. The optimized ultrathin CN nanosheet (~4 nm) exhibits excellent photoactivity with high selectivity (~99%). It is suggested that the excitonic energy transfer for 1O2 formation is close related to the intrinsic exciton binding energy and the two-dimensional quantum confinement effect. This work establishes a basic mechanistic understanding on the excitonic processes in CN, and develops a feasible route to design CN-based photocatalysts for efficient 1O2 generation.
Acetylene black (AB), as a kind of carbon material with large specific surface area, low density, strong electron transferability, is supposed to have great potential for application in advanced oxidation processes (AOPs). In this study, AB was utilized as a peroxydisulfate (PDS) activator for the catalytic degradation of sulfamethoxazole (SMX) in aqueous media. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) techniques, zeta potential and Raman spectra were employed to characterize the features of AB. To verify the excellent performance of AB/PDS systems, a series of control experiments were carried out. Compared to graphite/PDS and biochar/PDS system, AB/PDS system could complete degradation of SMX within 15 min. Besides, the effects of key factors including AB dosage, PDS dosage, initial pH and SMX concentration on SMX degradation in AB/PDS system were elucidated systematically. Furthermore, through the radical quenching experiments, it was proved that singlet oxygen (1O2) was dominantly responsible for the degradation of SMX. Finally, based on the experiment results and comprehensive analysis, a probable reaction mechanism of AB/PDS system for SMX degradation was proposed. This work suggests that AB has a good potential for tackling the hazardous pollutants in environmental remediation.
Here we report a facile defect-engineering strategy on the support to optimize the metal-support interaction and enhance the metal's electrocatalytic hydrodechlorination performance in converting 2, 4-dichlorophenol (2, 4-DCP) to phenol. The specific activity of the Pd nanoparticles (Pd NPs) on defective polymer carbon nitride (Pd/PCN-x) reaches 0.09 min-1 m-2Pd, which is 1.5 times that of the Pd NPs supported on the perfect PCN (Pd/PCN-0). The combined experimental and theoretical results demonstrate that the strong adsorption of phenol on Pd/PCN-0 passivates the active sites, limiting the dechlorination progress. The PCN-x containing -C≡N defects can effectively mediate the spatial configuration and electronic structure of Pd NPs, and promote the preferential adsorption of 2, 4-DCP rather than phenol, resulting in an enhanced dechlorination efficiency.
The porous g-C3N4 (PCN) nanosheets are successfully synthesized and further modified with nano-sized Ag by a simple wet-chemical process. Interestingly, the Ag-modified porous g-C3N4 (Ag-PCN) nanosheets exhibit competitive fluorescence detection performance of chloride ion (Cl-) in aqueous solution. Under the optimized conditions, the concentration of Cl- could be quantitative analyzed with the Ag-PCN in a wide detection range from 0.5 mmol/L to 0.1 mol/L, with a low detection limitation of 0.06 mmol/L. It is confirmed that the fluorescence of PCN could be effectively decayed by the photoinduced charge transfer via the adsorbed Cl- for trapping holes, mainly by means of the time-resolved fluorescence and surface photovoltage spectra. The porous structure and modified Ag promote the adsorption of Cl- on resulting Ag-PCN, leading to excellent fluorescence detection for Cl-. This work provides a feasible route to develop a fluorescence detection of Cl- with g-C3N4 nanosheets in environment water.
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