Complete arsenite removal from groundwater by UV activated potassium persulfate and iron oxide impregnated granular activated carbon

Arsenic removal from coal by ferric chloride enhanced leaching under ultraviolet irradiation during flue gas desulphurization with coal slurry

During coal combustion, the harmful element arsenic can be released into environment and cause potential significant harm to human beings. Therefore, it is very important to study the removal of arsenic from coal before combustion. In this work, simulated SO2-containing flue gas was used to leach arsenic from coal in a 1 L UV photoreactor. The effects of FeCl3, ultraviolet (UV), pH and the Cl-/Fe3+ molar ratio on arsenic leaching and SO2 removal were experimentally investigated and the enhancing mechanism was analysed. Experimental results demonstrated that FeCl3 and UV could efficiently increase iron and arsenic leaching percentages and SO2 removal efficiency. UV irradiation could induce the oxidation of most trivalent arsenic. The arsenic leaching percentage was significantly larger than that of iron. Low pH was favourable for iron and arsenic leaching. The optimal Cl-/Fe3+ molar ratio was determined to be 3:1. The introduced ferric chloride could not only increase the concentrations of free radicals and ferric iron oxidants, the chloride ion might also impede the formation of passive coatings, thus increasing the arsenic leaching percentage, intensifying the oxidation of trivalent arsenic and enhancing the removal of SO2.

Adsorptive-Photocatalytic Composites of α-Ferrous Oxalate Supported on Activated Carbon for the Removal of Phenol under Visible Irradiation

Adsorptive-photocatalytic composites based on activated carbon (AC) and α-ferrous oxalate dihydrate (α-FOD) were synthesized by an original two-step method and subsequently used for the removal of phenol from aqueous solutions. To obtain the composites, ferrotitaniferous black mineral sands (0.6FeTiO3·0.4Fe2O3) were first dissolved in an oxalic acid solution at ambient pressure, and further treated under hydrothermal conditions to precipitate α-FOD on the AC surface. The ratio of oxalic acid to the mineral sand precursor was tuned to obtain composites with 8.3 and 42.7 wt.% of α-FOD on the AC surface. These materials were characterized by X-ray powder diffraction, scanning electron microscopy, and the nitrogen adsorption-desorption method. The phenol removal efficiency of the composites was determined during 24 h of adsorption under dark conditions, followed by 24 h of adsorption-photocatalysis under visible light irradiation. AC/α-FOD composites with 8.3 and 42.7 wt.% of α-FOD adsorbed 60% and 51% of phenol in 24 h and reached a 90% and 96% removal efficiency after 12 h of irradiation, respectively. Given its higher photocatalytic response, the 42.7 wt.% α-FOD composite was also tested during successive cycles of adsorption and adsorption-photocatalysis. This composite exhibited a reasonable level of cyclability (~99% removal after four alternated dark/irradiated cycles of 24 h and ~68% removal after three simultaneous adsorption-photocatalysis cycles of 24 h). The promising performance of the as-prepared composites opens several opportunities for their application in the effective removal of organic micropollutants from water.

Fast and efficient As(III) removal from water by bifunctional nZVI@NBC

As a notable toxic substance, metalloid arsenic (As) widely exists in water body and drinking As-contaminated water for an extended period of time can result in serious health concerns. Here, the performance of nanoscale zero-valent iron (nZVI) modified N-doped biochar (NBC) composites (nZVI@NBC) activated peroxydisulfate (PDS) for As(III) removal was investigated. The removal efficiencies of As(III) with initial concentration ranging from 50 to 1000 μg/L were above 99% (the residual total arsenic below 10 μg/L, satisfying the contaminant limit for arsenic in drinking water) within 10 min by nZVI@NBC (0.2 g/L)/PDS (100 μM). As(III) removal efficiency influenced by reaction time, PDS dosage, initial concentration, pH, co-existing ions, and natural organic matter in nZVI@NBC/PDS system were investigated. The nZVI@NBC composite is magnetic and could be conveniently collected from aqueous solutions. In practical applications, nZVI@NBC/PDS has more than 99% As(III) removal efficiency in various water bodies (such as deionized water, piped water, river water, and lake water) under optimized operation parameters. Radical quenching and EPR analysis revealed that SO4·- and ·OH play important roles in nZVI@NBC/PDS system, and the possible reaction mechanism was further proposed. These results suggest that nZVI@NBC activated peroxydisulfate may be an efficient and fast approach for the removal of water contaminated with As(III).

Recent progress in chromium removal from wastewater using covalent organic frameworks - A review

Covalent organic frameworks (COFs) offer a pivotal solution to urgently address heavy metal removal from wastewater due to their exceptional attributes such as high adsorption capacity, tunable porosity, controllable energy band structures, superior photocatalytic performance, and high stability-reusability. Despite these advantages, COFs encounter certain challenges, including inefficient utilization of visible light, rapid recombination of photogenerated carriers, and limited access to active sites due to close stacking. To enhance the photocatalytic and adsorptive performance of COF-based catalysts, various modification strategies have been reported, with a particular focus on molecular design, structural regulation, and heterostructure engineering. This review comprehensively explores recent advancements in COF-based photocatalytic and adsorptive materials for chromium removal from wastewater, addressing kinetics, mechanisms, and key influencing factors. Additionally, it sheds light on the influence of chemical composition and functional groups of COFs on the efficiency of hexavalent chromium [Cr (VI)] removal.

Insights on volatile metals in landfill gas as determined from advanced treatment media

This study analyzed spent activated carbon (AC) from a landfill gas (LFG) treatment system for an expanded suite of lesser studied volatile metals, revealing elevated levels of As and Sb in the LFG, exceeding those previously reported, with minimum average concentrations of 640 µg m-3 and 590 µg m-3, respectively. The annual release of As and Sb through landfill gas was found to be significant, surpassing leachate emissions by an order of magnitude. Extrapolating these findings to all US landfills suggests that the release of As and Sb through landfill gas could be a major, previously overlooked source of these metals in global emission estimates, underscoring the need to include them when developing future inventories. The spent AC was further found to exceed US toxicity limits established for As, classifying it as hazardous waste under US regulations. However, findings suggest that the AC scrubber employed at the landfill effectively prevented substantial releases of As and Sb. This research emphasizes that landfill gas is a primary contributor to environmental release of As and Sb from landfills, even more so than leachate, highlighting the significance of implementing effective LFG treatment measures to mitigate the release of volatile metal emissions.

Fabrication of water-floating litchi-like polystyrene-sphere-supported TiO2/Bi2O3 S-scheme heterojunction for efficient photocatalytic degradation of tetracycline

The exploration of advanced photocatalysts for antibiotic degradation is critical, but it remains a challenge due to the lack of rational structural design and in-depth insights into molecular oxygen activation. Water-floating photocatalysts could be one of the best choices owing to their technical features in terms of reasonability and efficiency involving a high oxygenation of photocatalyst surface, fully solar irradiation, and simple recycling and reuse. Herein, a floatable litchi-like architecture of a polystyrene-sphere-supported TiO2/Bi2O3 (PS@TiO2/Bi2O3) S-scheme heterojunction was skillfully constructed and evaluated for photodegradation of model tetracycline (TC) antibiotics. By integrating the advantages of floatability and S-scheme, the TC removal rate of the optimal PS@TiO2/Bi2O3-0.4 catalyst can reach 88.4% under 1 h illumination, which is higher than that of pristine Bi2O3 (60.8%) and PS@TiO2 (40.1%). Moreover, PS@TiO2/Bi2O3-0.4 exhibits high recyclability and stability, and there is no significant loss of activity after five cycles of repeated use. With the aid of liquid chromatography-mass spectrometry analysis and density functional theory calculations, a reasonable degradation pathway for TC was proposed. The present work provides a recyclable and efficient approach for the photodegradation of TC, expecting to guide the innovative exploitation of other environmental systems.

Aniline degradation and As (III) oxidation and immobilization by thermally activated persulfate

In the Pearl River Delta of China, many sites are likely contaminated with aniline in the soil and arsenic (As) in the groundwater because of a high As background level and the prevailing printing and dyeing industry. This study is to explore the remediation performance of thermally activated persulfate oxidation for the sites with these two contaminants, aniline and As. The As influence on the aniline degradation and vice versa are also systematically investigated. When the molar ratio of aniline to persulfate is 1: 4.65, over 85% of aniline can be degraded at 40 °C in 24 h, and 100 μg L-1 As(III) in solution can be completely adsorbed by the soil. A higher pH favored the aniline degradation but disfavored the As(III) oxidation. Due to the strong buffer capacity of the soil, aniline in the soil could be more quickly degraded than those in the solution. The As(III), however, seem more easily oxidized in the absence of soil. The coexisting Fe2+ can substantially improve As(III) oxidation and immobilization, although the dilute Fe2+ solution may suppress the aniline degradation. The presence of aniline severely inhibited the As(III) oxidation and adsorption, likely due to the competition for the generated free radicals and the adsorption sites on the soils. In contrast, the existing As(III) has a slight effect on aniline degradation. These findings are believed to provide the theoretical basis for the remediation of aniline-arsenic contaminated sites.

Landfill gas as a source of anthropogenic antimony and arsenic release

Antimony is used extensively in consumer goods, including single use plastic bottles, electronics, textiles and automobile brakes, which are disposed of in landfills at the end of their service lives. As a result, Sb is a constituent of concern in landfill emissions. Previous research has focused on leachate (liquid) and waste incineration flue gas emissions; however, Sb has the potential to volatilize through chemical and microbial processes within a landfill. In this study, iron-amended granular activated carbon was used to adsorb volatile metals directly from gas in a full-scale landfill gas collection system. Metals were quantified using acid digestion and ICP-AES analysis. Antimony concentrations far exceeded those previously reported, at up to 733 μg m^-3 (mean: 254 μg m^-3). In addition to Sb, As was also measured at high levels compared to previous research, as high as 740 μg m^-3 (mean: 178 μg m^-3). Using US EPA landfill and landfill gas databases, total Sb emissions via landfill gas are estimated to be approximately 27.3 kg day^-1 in the US. Based on other estimates of national and global Sb emissions, this corresponds to approximately 4.5% of total US atmospheric emissions of Sb and 0.42% of global atmospheric emissions. Sb mass release via landfill gas is approximately 3.9 times higher than via leachate emissions. Although gas emissions are higher than expected, the vast majority (99.9%) of Sb present in landfilled MSW remains within the waste mass indefinitely. In addition to these mass release estimates, this experiment suggests that iron-amended activated carbon may offer significant metals removal from LFG, especially in the first months of new well operation.

Revealing the charge transfer mechanism in magnetically recyclable ternary g-C3N4/BiOBr/Fe3O4 nanocomposite for efficient photocatalytic degradation of tetracycline antibiotics

Pharmaceutical compounds in water bodies pose hazards to the ecosystem because of their biotoxicity potency. To eradicate such pharmaceutical compounds, a novel g-CN/BiOBr/Fe₃O₄ nanocomposites was prepared using a simplistic route and appraised for photodegradation of model tetracycline antibiotics. The g-CN/BiOBr/Fe₃O₄ nanocomposites exhibited complete tetracycline degradation in just 60 min exposure of simulated light irradiation, which is 6 times higher than the g-CN. Under the analogous condition, the tetracycline mineralization ability of the g-CN/BiOBr/Fe₃O₄ nanocomposites was evaluated to be 78% of total organic carbon removal. The superior photocatalytic performance is ascribed to the extended visible light harvesting ability and enhanced charge carrier separation/transfer with impeded recombination rate in light of effective indirect Z-scheme heterojunction construction. Based on band-edge potential and radical trapping studies indicate that h⁺ > •O₂^- > •OH are the active species responsible for photodegradation. Furthermore, the ternary nanocomposites are magnetically retrievable and recyclable while retaining their stable photocatalytic performance. This work endows a new perspective on the rational design and construction of magnetically recoverable ternary nanocomposite for environmental remediation.

Effect of applying persulfate on the accumulation of arsenic in rice plants grown in arsenic-contaminated paddy soil

Arsenic is known to be a notorious human carcinogen and rice consumption is becoming the primary human exposure route for As, especially in many Asian countries. As one of redox-sensitive elements in soil, sulfur plays an indisputable role in controlling As behaviors. However, information on the effects of persulfe (PS) on the toxicity and accumulation of As in rice plant under flooded conditions is limited. Therefore, a pot experiment was conducted to investigate the effects of PS amendment on the growth and accumulation of As species in rice plants grown in As-contaminated paddy soil. Results revealed that PS application increased the As, Fe, and Mn in porewater at the early stage, and then declined. Application of PS increased the biomass of stem and root, while inhibited the formation of iron plaque on the root surface. The As translocation from root to rice above tissues and accumulation of As species in brown rice were declined by amendment with PS. The inorganic arsenic (iAs) and DMA were the two main species in brown rice, and decreased by 13~26% and 40~60% respectively upon PS application. The results suggested that amendment with PS might be feasible for reducing the accumulation of As in rice grains grown in As-contaminated paddy soil. However, further detailed studies on the potential soil biogeochemical and physiological mechanisms are recommended.

Chemiluminescence based on UV-assisted persulfate activation for sensitive detection of triphenyl phosphate

Triphenyl phosphate (TPHP), a typical kind of organophosphorus flame retardants (OPFRs) with aryl groups, has been recognized as an emerging contaminant that causes environmental and health hazards. It is a pervasive threat that can be frequently detected in the environment and living organisms. Hence, establishing an efficient analytical method for TPHP is an urgent issue. In this work, a heteropolyacid (HPA)-luminol chemiluminescence strategy coupled with UV-assisted persulfate (PS) activation was proposed for the sensitive and selective detection of TPHP. The UV-assisted PS oxidation pretreatment could decompose the water-insoluble TPHP into smaller orthophosphates, which were further converted into HPA with the subsequently introduced vanadium‑molybdenum acid. The formed HPA served as a catalyst to oxidize luminol, and strong chemiluminescence at 425 nm was generated immediately. Furthermore, the degradation process of TPHP and chemiluminescence mechanism were also investigated. The results demonstrated that some reactive oxygen radicals such as SO₄^-, OH, ¹O₂, and O₂^-, were involved in the degradation and chemiluminescence reaction. Notably, this proposed chemiluminescence analytical strategy realized a highly sensitive detection for TPHP, and granted the limit of detection down to 0.38 ppt. This study provides an attractive perspective for the detection of emerging OPFRs.

Revealing the stability of CuWO4/g-C3N4 nanocomposite for photocatalytic tetracycline degradation from the aqueous environment and DFT analysis

Graphitic carbon nitride (g-C₃N₄) is an emerging metal-free photocatalyst, however, engineering the photocatalytic efficiency for the effective degradation of hazardous molecules is still challenging. An unstable and low bandgap CuWO₄ was composited with g-C₃N₄ to achieve synergistic benefits of tuning the visible light responsiveness and stability of CuWO₄. CuWO₄/g-C₃N₄ nanocomposite exhibited a relatively high visible light absorption region and the bandgap was modified from 2.77 to 2.53 eV evidenced via UV-DRS. Moreover, the fast electron transfer rate was observed with CuWO₄/g-C₃N₄ nanocomposite as confirmed using PL and photocurrent studies. XRD, FT-IR, and HR-TEM analyses signified the formation of CuWO₄/g-C₃N₄ nanocomposite. CuWO₄/g-C₃N₄ nanocomposite showed enhanced photocatalytic degradation of Tetracycline (TC) about ∼7.4 fold greater than pristine g-C₃N₄ in 120 min. Notably, the OH^• and ^•O₂^- radicals played a most significant role in photocatalytic TC degradation. Furthermore, the energy band structure, density of state, and Bader charge analyses of these molecules were performed.

Complete removal of Tetracycline by sonophotocatalysis using ultrasound-assisted hierarchical graphitic carbon nitride nanorods with carbon vacancies

Tuning a graphitic carbon nitride (CN) structure is an effective strategy to advance its physicochemical and electronic properties. Herein, hierarchical CN nanorods with carbon vacancy were synthesized via ultrasound-assisted thermal polycondensation method wherein melamine-HONH₂·HCl complex acts as a template. The hierarchical CN nanorods can facilitate multiple light scattering, provide large specific surface area with extensive reactive sites and endow abundant mass-transport channels for charge migration. The existence of carbon vacancies can serve as shallow charge trapping sites and prompt charge separation. Consequently, hierarchical CN nanorod possessed excellent sonophotodegradation efficiency of ∼100% towards Tetracycline (TC) antibiotic within 60 min under ultrasonic irradiation and visible light illumination. Moreover, the sonophotocatalytic degradation was higher than the sum of sonocatalytic and photocatalytic TC degradation using hierarchical CN nanorods due to its synergistic performance. A plausible sonophotocatalytic mechanism and TC degradation pathway using hierarchical CN nanorod were proposed. Lastly, hierarchical CN nanorod is durable and stable which can withstand the sonophotocatalytic condition even after the fifth run. This work offers an insight into hierarchical CN nanorod to advance sonophotocatalytic degradation performance for highly efficient removal of various recalcitrant pollutants.

Construction of S-scheme 1D/2D rod-like g-C3N4/V2O5 heterostructure with enhanced sonophotocatalytic degradation for Tetracycline antibiotics

Pharmaceutically active compounds are an emerging water contaminant that resists conventional wastewater treatments. Herein, the sonophotocatalytic degradation of Tetracycline (TC) antibiotics as a model contaminant was carried out over a rod-like g-C₃N₄/V₂O₅ (RCN-VO) nanocomposite. RCN-VO nanocomposite was synthesized via ultrasound-assisted thermal polycondensation method. The results showed that the RCN-VO nanocomposite could completely remove the TC in water within 60 min under simultaneous irradiation of visible light and ultrasound. Moreover, the sonophotocatalytic TC degradation (a synergy index of ∼1.5) was superior to the sum of individual sonocatalytic and photocatalytic degradation using RCN-VO nanocomposite. Besides, the enhanced sonophotocatalytic activity of RCN-VO can be attributed to the 1D/2D nanostructure and the S-scheme heterojunction formation between RCN and VO where the electrons migrated from RCN to VO across the RCN-VO interface. Under irradiation, the built-in electric field, band edge bending and Coulomb interaction can synergistically facilitate the unavailing electron-hole pair recombination. Thereby, the cumulative electron in RCN and holes in VO can actively take part in the redox reaction which generates free radicals and attack the TC molecules. This study provides insight into a novel S-Scheme heterojunction photocatalyst for the removal of various refractory contaminants via sonophotocatalytic degradation.

Core-Shell Fe2O3@La1-xSrxFeO3-δ Material for Catalytic Oxidations: Coverage of Iron Oxide Core, Oxygen Storage Capacity and Reactivity of Surface Oxygens

A series of Fe2O3@LSF (La0.8Sr0.2FeO3-δ perovskite) core-shell materials (CSM) was prepared by infiltration of LSF precursors gel containing various complexants and their mixtures to nanocrystalline aggregates of hematite followed by thermal treatment. The content of LSF phase and amount of carboxyl groups in complexant determine the percent coverage of iron oxide core with the LSF shell. The most conformal coating core-shell material was prepared with citric acid as the complexant, contained 60 wt% LSF with 98% core coverage. The morphology of the CSM was studied by HRTEM-EELS combined with SEM-FIB for particles cross-sections. The reactivity of surface oxygen species and their amounts were determined by H2-TPR, TGA-DTG, the oxidation state of surface oxygen ions by XPS. It was found that at complete core coverage with perovskite shell, the distribution of surface oxygen species according to redox reactivity in CSM resemble pure LSF, but its lattice oxygen storage capacity is 2-2.5 times higher. At partial coverage, the distribution of surface oxygen species according to redox reactivity resembles that in iron oxide.