In-situ groundwater remediation of contaminant mixture of As(III), Cr(VI), and sulfanilamide via electrochemical degradation/transformation using pyrite.

Electrochemical advanced oxidation processes (EAOPs) are effective in removing persistent contaminants from groundwater. However, their practical applicability depends significantly on various site-specific characteristics. Therefore, the primary objective of this investigation was to study the feasibility of EAOPs and pyrite, which is a sulfide mineral, to effectively remove the mixture of arsenic (As (III)), chromium (Cr (VI)), and sulfanilamide in groundwater. We conducted a comparison of three systems: (1) EAOP alone, (2) pyrite alone, and (3) a combined EAOP and pyrite system. In EAOP alone, sulfanilamide was effectively oxidized (80%), while the electrochemical transformation of As(III)/Cr(VI) into As(V)/Cr(III) was limited. In just the pyrite system, As(III), Cr(VI), and sulfanilamide were adsorbed onto the surface of pyrite (60%, 20%, and 18%). Neither the EAOP nor the pyrite system alone could effectively treat the contaminants mixture. Nonetheless, the combined system completely removed As(III), Cr(VI), and sulfanilamide by the synergistic reaction. This could be attributed to the formation of green rust, a natural adsorbent mineral produced as a reaction of dissolved iron, generated via electrochemical pyrite oxidation, with the groundwater electrolyte (e.g., CO3 or SO4). This system harmonized the combined approach of EAOP and pyrite to effectively eliminate both organic and inorganic contaminants. ENVIRONMENTAL IMPLICATION: A paper proposed electrochemical oxidation (EO) with pyrite to remove both organic and inorganic contaminants from groundwater. The removal performance of the combined system was evaluated, and the synergistic mechanism was revealed. The combination of EO and pyrite with synergistic removal effectively removed the mixture of both contaminants. This could be attributed by the formation of green-rust by electrochemical activation for pyrite. Compared to the single system of EO and pyrite alone, the combined system with EO and pyrite improved removal performance. Results suggested that the combined system could be used for green groundwater remediation.

Adsorption of antibiotics onto low-grade charcoal in the presence of organic matter: Batch and column tests.

Antibiotics contaminate diverse ecosystems and threaten human health. In ecosystems including water, sediment, and soil, the amount of antibiotics present is tiny compared to the amount of natural organic matter. However, most studies have ignored the co-presence of natural organic matter in the adsorption of target antibiotics. In this study, we quantitatively evaluated the effect of co-presenting natural organic matter on the adsorption of sulfamethazine (SMZ) through batch and column experiments using low-grade charcoal, an industrial by-product. SMZ was used as a model antibiotic compound and humic acid (HA) was used to represent natural organic matter. The co-presence of 2000 mg/L HA (400 times the concentration of SMZ) lowered the adsorption rate of SMZ from 0.023 g/mg·min to 0.007 g/mg·min, and the maximum adsorption capacity from 39.8 mg/g to 15.6 mg/g. HA blocked the charcoal's pores and covered its surface adsorption sites, which dramatically lowered its capacity to adsorb SMZ. Similar results were obtained in the flow-through column experiments, where the co-presence of natural organic matter shortened the lifetime of the charcoal. As a result, the co-presence of a relatively high concentration of natural organic matter can inhibit the adsorption of SMZ and likely other antibiotic compounds, and thus the presence of natural organic matter should be accounted for in the design of adsorption processes to treat antibiotics in water.

Electrochemical oxidation and mechanism of sulfanilamide from groundwater in a flow-through system using carbon fiber (CF) anode.

Metal-based anodes have been used for a long time in the electrochemical oxidation processes to remediate groundwater. However, the high cost of this technique as well as the release of potentially toxic metals (ex, lead), are major barriers being fully implemented. As an alternative of metal-based anodes, in recent years, carbon-based anodes have been paid attention due to their eco-friendliness and cost-effectiveness. This study evaluated the oxidation performance of carbon fiber (CF) anode in a flow-through system. The CF anode degraded 45-87% of the target pollutant (sulfanilamide), depending on the current intensity applied. However, no further degradation of sulfanilamide was observed after the cathode, indicating that sulfanilamide degradation occurred mainly at the anode. This study also determined the effect of electrolytes on electrochemical oxidation using chloride (Cl-), sulfate (SO42-), bicarbonate (CO3-), and synthetic groundwater. Cl- and SO42- electrolytes were converted electrochemically into active species, thereby enhancing sulfanilamide degradation, while the bicarbonate and groundwater electrolytes inhibited oxidation performance by scavenging hydroxyl radicals. A series of scavenger tests and characterization showed that the direct oxidation and hydroxyl radicals involved the sulfanilamide degradation. Especially, the production of hydroxyl radicals is more favorable in high currents than in low currents. That is, CF anode contributed to the degradation by direct oxidation of carbon-based electrodes and generation of hydroxyl radicals. In summary, this study highlights how a CF anode is capable of effectively degrading organic pollutants via anodic oxidation.

In-situ hydrogen peroxide formation and persulfate activation over banana peel-derived biochar cathode for electrochemical water treatment in a flow reactor.

Electrochemical advanced oxidation processes (EAOPs) are effective for the removal of organic contaminants from groundwater. The choice of an affordable cathode material that can generate reactive oxygen species (ROS) such as hydrogen peroxide (H2O2) and hydroxyl radicals (•OH) will increase practicality and cost effectiveness of EAOPs. Carbon enriched biochar (BC), which is derived from pyrolysis of biomass, has emerged as an inexpensive and environmentally-friendly electrocatalyst for removing contaminants from groundwater. In this study, a banana peel-derived biochar (BP-BC) cathode packed in a stainless steel (SS) mesh was used in a continuous flow reactor to degrade the ibuprofen (IBP), as a model contaminant. The BP-BC cathodes generate H2O2 via a 2-electron oxygen reduction reaction, initiate the H2O2 decomposition to generate •OH, adsorb IBP from contaminated water, and oxidize IBP by formed •OH. Various reaction parameters such as pyrolysis temperature and time, BP mass, current, and flow rate, were optimized to maximize IBP removal. Initial experiments showed that H2O2 generation was limited (∼3.4 mg mL-1), resulting in only âˆ¼ 40% IBP degradation, due to insufficient surface functionalities on the BP-BC surface. The addition of persulfate (PS) into the continuous flow system significantly improves the IBP removal efficiency via PS activation. The in-situ H2O2 formation and PS activation over BP-BC cathode results in concurrent generation of •OH and sulfate anion radicals (SO4•-, a reactive oxidant), respectively, which collectively achieve âˆ¼ 100% IBP degradation. Further experiments with methanol and tertiary butanol as potential scavengers for •OH and SO4•- confirm their combined role in complete IBP degradation.

Novel electrochemical method to activate biochar derived from spent coffee grounds for enhanced adsorption of lead (Pb).

Biochar (BC) has received much attention as a promising adsorbent that can be exploited to remove heavy metals in domestic and wastewater. The adsorption capacity of BC is, however, relatively low compared to that of conventional adsorbents, and its performance is inversely proportional to its stability. Various chemical and physical methods have been tried to address these limitations, but BC activation still generates too much acidic or alkaline wastewater. Here we propose a novel electrochemical method and compare its lead (Pb) adsorption capacity to that of acid- and alkaline-based approaches. We found that electrochemical activation significantly increased the number of hydroxyl and carboxylic groups on the BC surface, which led to an increase in Pb absorption from 27 % (pristine BC) to 100 % because the oxygenated-functional groups contributed to the adsorption of Pb. Pb capacity was 1.36, 2.64, 3.31, and 5.00 mg g-1, corresponding to pristine, acidic, alkaline, and electrochemical activation, respectively. The Pb absorption capacity of electrochemically activated BC was also higher than that of acid- and alkali-activated BC, which we attribute to the observed increases in oxygen ratio and surface area. Moreover, the adsorption rate of BC after electrochemical activation was 190 times faster and its capacity was 2.4 times higher than that of pristine BC. These findings show that the electrochemical activation of BC results in greater adsorption capacity than conventional methods.

Mitigation of arsenic release by calcium peroxide (CaO2) and rice straw biochar in paddy soil.

Biochar has a great potential in the stabilization of soil heavy metals; however, the application can actually enhance the mobility of Arsenic (As) in soil. Here, a biochar-coupled calcium peroxide system was proposed to control the increase in As mobility caused by biochar amendment in paddy soil environment. The capability of rice straw biochar pyrolyzed at 500 °C (RB) and CaO2 to control As mobility was evaluated by incubation for 91 days. CaO2 encapsulation was performed for pH control of CaO2, and As mobility was evaluated using a mixture of RB + CaO2 powder (CaO2-p), and RB + CaO2 bead (CaO2-b), respectively. The control soil solely and RB alone were included for comparison. The combination of RB with CaO2 exhibited remarkable performance in controlling As mobility in soil, and As mobility decreased by 40.2% (RB + CaO2-p) and 58.9% (RB + CaO2-b) compared to RB alone. The result was due to high dissolved oxygen (6 mg L-1 in RB + CaO2-p and RB + CaO2-b) and calcium concentrations (296.3 mg L-1 in RB + CaO2-b); oxygen (O2) and Ca2+ derived from CaO2 is able to prevent the reductive dissolution and chelate-promoted dissolution of As bound to iron (Fe) oxide by biochar. This study revealed that the simultaneous application of CaO2 and biochar could be a promising way to mitigate the environmental risk of As.

Covalent immobilizing horseradish peroxidase on electrochemically-functionalized biochar for phenol removal.

Enzyme-based biocatalytic treatment has been known as an effective measure to biologically degrade organic pollutants. Advantageously, enzymes could be immobilized on solid supports, and such fact enables reuse/prolong the enzymatic capability. It could be of great importance to functionalize a support material for enhancing the immobilization efficiency/stability of enzymes. As such, this study laid great emphasis on covalent bonding to immobilize horseradish peroxidase (HRP) on a functionalized rice straw biochar with glutaraldehyde (GA) as a crosslinker. Biochar was pretreated by the electrochemical method and the acid treatment respectively to enrich the oxygen-containing functional groups. These led to the enhanced immobilizing ability of biochar. The HRP immobilized on the electrochemically-functionalized biochar (HRP-EBC) showed three times as much enzyme activity as the HRP directly adsorbed onto biochar. The HRP immobilized on the acid-functionalized biochar (HRP-ABC) showed activity similar to that of HRP-EBC. It was concluded that both the (acid/electrochemical) pretreatments are effective to enhance enzyme immobilization. Nevertheless, the electrochemical functionalized method of biochar is chemical oxidant-free, and one important lesson from a series of tests was that the pretreatment of biochar through the electrochemical method could be more environmentally benign. Moreover, employing HRP-EBC could be beneficial from a perspective of a real environmental practice considering its higher pH, thermal stability, and good reusability. 80% of phenol was degraded in 1 h in the presence of HRP-EBC when pH was 7.0 and a ratio of H2O2 to phenol was 1:1.5.

Mechanistic investigation into flow-through electrochemical oxidation of sulfanilamide for groundwater using a graphite anode.

The technical effectiveness/merit of electrochemical oxidation (EO) has been recognized. Nonetheless, its practical application to groundwater remediation has not been fully implemented due to several technical challenges. To overcome the technical incompleteness, this study adopted a graphite anode in the flow-through system and studied the mechanistic roles of a graphite anode. To this end, groundwater contaminated with sulfanilamide was remediated by means of EO, and sulfanilamide oxidation was quantitatively determined in this study. Approximately 60% of sulfanilamide was degraded at the anode zone, and such observation offered that the removal of sulfanilamide was not closely related with current variations (10-100 mA). However, this study delineated that sulfanilamide removal is contingent on the flow speed. For example, the removal of sulfanilamide was lowered from 59 to 25% owing to a short contact time when the flow velocity was increased from 0.14 to 0.55 cm/min. This study also delineated that a shorter anode-cathode distance could offer a favorable chance to enhance the removal of sulfanilamide even under an identical current. A shorter distance could offer a chance to save energy due to the lower voltage operation. This study also offered that chloride (Cl-) and sulfate (SO42-) electrolytes served a crucial role in the generation of active species. In contrast, bicarbonate (HCO3-) and synthetic groundwater electrolytes impeded the oxidation rate because HCO3- scavenged the other active species. In an effort to seek the oxidation mechanisms of a graphite anode, scavenger, cyclic voltammetry test, and electron https://en.wikipedia.org/wiki/Electron_paramagnetic_resonanceparamagnetic resonance (EPR) analysis were done. From a series of the tests, it was inferred that a graphite anode did not directly affect the generation of the active species. Thus, the prevalence of the oxygenated functional groups on an anode surface could be the main mechanism in sulfanilamide removal due to the enhanced electron transfer.

CaO2-based electro-Fenton-oxidation of 1,2-dichloroethane in groundwater.

It has been well recognized that the Fenton reaction requires a rigorous pH control and suffers from the fast self-degradation of H2O2. In an effort to resolve the technical demerits of the conventional Fenton reaction, particular concern on the use of CaO2-based Fenton reaction was paid in this study. To realize the practical use of CaO2 in the Fenton reaction for groundwater remediation, it could be of great importance to control its reaction rate in the subsurface. As such, this study laid great emphasis on the combined process of electrochemical oxidation and CaO2-based Fenton oxidation, using 1,2-dichloroethane (1,2-DCA) as a model compound. It was hypothesized that the reaction rate is also highly contingent on the formation of Fe(II) (stemmed from iron anode oxidation). Eighty percent of 1,2-DCA were degraded by the CaO2-based Fenton reaction. The final pH was neutral, inferring that the reaction could be a viable option for the subsurface environment. Moreover, the supply of electric current in an iron anode expedited 1,2-DCA degradation efficiency from 35 % to 62 % via electrically generated Fe(II), which donated electrons to H2O2, producing more hydroxyl radicals. An anode-cathode configuration from the single-well system enhanced the degradation of 1,2-DCA, with less amount of energy consumption than the double-well system. Based on results, CaO2-based electro-Fenton oxidation can remove well 1,2-DCA in groundwater and can be a strategic measure for groundwater remediation.

Control of arsenic release from paddy soils using alginate encapsulated calcium peroxide.

The mobilization of As in paddy soils is affected by iron redox cycles. In this regard, calcium peroxide (CaO2) can be used as an alternative to maintaining oxidizing conditions by liberating oxygen under flooding environments. Nevertheless, the problem of increase in pH by CaO2 dissolution remains unresolved. In this study, the encapsulation of CaO2 using alginate is proposed. Encapsulated CaO2 (CaO2-b) using 1% sodium alginate was applied to As-contaminated soil to evaluate the ability of pH control and As mobility during flooding conditions. The pH increased rapidly from 6.8 to 9.0 in unencapsulated CaO2 (CaO2-p) within 1 day, while CaO2-b increased slowly to 8.6 over 91 days. CaO2 created an oxidizing condition in the soil by providing oxygen, thus effectively prevented the reductive dissolution of iron. The mobility of As decreased by 50% (CaO2-p) and 83% (CaO2-b) compared with that of the control soil. Furthermore, the As in pore water was three times lower than CaO2-p because CaO2-b released 1.8 times more Ca2+ to form Ca-As complexes than CaO2-p. Consequently, the encapsulated CaO2 reduced the negative effects of CaO2 treatment on increasing pH of the soil and furnished a better environmental condition for inhibiting As mobility.

Removal of 1,2-dichloroethane in groundwater using Fenton oxidation.

Among the chlorinated aliphatic hydrocarbons, 1,2-dichloroethane (1,2-DCA) is widely used for the synthesis of vinyl chloride monomers. Despite the high demand for 1,2-DCA, it poses a risk to the environment because it is persistent and carcinogenic. Therefore, in this study, several reagents (dithionite, hydrosulfide, sulfite, persulfate, sulfate radicals, and hydroxyl radicals) were evaluated for the degradation of 1,2-DCA. Among these, the hydroxyl radicals generated by the Fenton reaction were the most suitable oxidant, decomposing 92% of 1,2-DCA. Chloride, one of the final oxidized products, was observed, which supported the oxidation reaction. Moreover, with an increasing concentration of hydroxyl radicals, the degradation of 1,2-DCA increased. Furthermore, sufficient amounts of hydrogen peroxide were more important than Fe(II) in the decomposition of 1,2-DCA. The radical reaction can generate larger molecules via the degradation of 1,2-DCA, which are degraded over time. The applicability of Fenton oxidation was evaluated using real 1,2-DCA-contaminated groundwater. Although the degradation of target contaminant was lowered due to the alkaline pH and the presence of chloride and bicarbonate ions in groundwater, the Fenton reaction was still efficient to oxidize 1,2-DCA. These results indicate that Fenton oxidation is an effective technique for the treatment of 1,2-DCA in contaminated groundwater.

Simultaneous oxidation and analysis of TOC-TN-TP in one pot reactor.

Total organic carbon (TOC), total nitrogen (TN), and total phosphorous (TP) are the most common indicators of water quality. The analytical processes of the indicators require oxidation of any type of C, N, and P to carbon dioxide, nitrate, and phosphate as final products. Persulfate is the recommended oxidant for these transformations. In this study, co-oxidation was suggested for the simultaneous analysis of TOC-TN-TP. A single oxidizing reactor using persulfate was proposed instead of three individual systems. The system oxidizes complex organic chemicals to carbon dioxide, nitrate, and phosphate. However, the residual persulfate after oxidation interferes with the spectrophotometric analysis of nitrate and phosphate. Therefore, in the proposed system, the complete transformation of persulfate is a key factor for simultaneous analysis. In this system, ultraviolet irradiation for 30 min under alkaline conditions converted residual persulfate to sulfate. The complete transformation eliminated persulfate interference in nitrate and phosphate detection. In the proposed system with a single oxidation reactor, TOC, TN, and TP were oxidized and analyzed simultaneously within 15% of the analytical error range compared to the standard test method.

Reduction of nitrate using biochar synthesized by Co-Pyrolyzing sawdust and iron oxide.

Nitrate is the most common contaminant in groundwater in Korea, as well as across the world. Reduction of nitrate to ammonia is one of the options available to remediate groundwater. In this study, nitrate in groundwater was removed using a zero-valent iron (ZVI) containing biochar synthesized by co-pyrolyzing iron oxide and sawdust biomass. Among the various biogases generated during the pyrolysis of biomass, CO and H2 act as reducing agents to transform iron oxides to ZVI. Approximately 71% of nitrate was reduced to ammonium by ZVI-biochar at initial pH 2.0, and the reduction decreased sharply by the increase in pH. The mass of nitrate-N decreased is exactly same with the mass of ammonia-N formed. However, ammonium remained in the aqueous phase after reduction by ZVI-biochar, and the total nitrogen was not lowered. Acid-washed zeolite adsorbed most ammonium reduced by the ZVI-biochar and maintained the pH to acidic condition to facilitate the reduction of nitrate. The results of this study imply that nitrate-contaminated groundwater can be properly treated within the guidelines of water quality by synthesized ZVI-containing biochar.

Enhanced-oxidation of sulfanilamide in groundwater using combination of calcium peroxide and pyrite.

Fenton reaction using hydrogen peroxide (H2O2) has been widely applied to achieve the in-situ chemical oxidation of contaminated soil and groundwater. However, injecting and transporting H2O2 to a contaminated zone consumes the chemical through reactions with other substances and self-decomposition. Additionally, Fe(II), an activator for the Fenton reaction, scavenges hydroxyl radicals, greatly reducing its activity. Therefore, this study proposes a novel oxidation system combining calcium peroxide (CaO2) and pyrite for the degradation of oxidizable contaminants in groundwater. CaO2 is an oxygen releasing compound, and pyrite is a natural mineral that provides Fe(II). The individual applications of CaO2 and pyrite cannot generate OH radicals and oxidize the target pollutant, sulfanilamide. However, the combination of pyrite and CaO2 oxidized well sulfanilamide even in mild pH and 1.0 wt% of pyrite. Moreover, H2O2 and OH radicals are the dominant oxidants in the reaction. A speciation analysis shows the oxidation of pyrite in this combined system. Furthermore, this system oxidized 80% of 0.1 mM sulfanilamide, whereas only 30% was oxidized by conventional Fenton reaction, indicating that this combined system is effective and applicable to remediate groundwater. This study provides an alternative oxidation process to achieve in-situ chemical oxidation.

In-situ generation of reactive oxygen species using combination of electrochemical oxidation and metal sulfide.

In-situ chemical oxidation (ISCO) is commonly practiced to degrade organic pollutants in various fields. However, ISCO is deteriorated the oxidation efficiency due to the non-selective and self-decomposition of reagents. Therefore, in-situ generation of oxidants is being proposed to compensate for the demerits of conventional ISCO. In this study, the aim is to suggest a novel in-situ generation system using the combination of electrochemical oxidation (EO) and pyrite oxidation. It is hypothesized that EO system can generate the oxygen species, which can activate the pyrite surface to produce more oxidants. We evaluated three systems (1) EO system (2) pyrite oxidation system (3) combined system using sulfanilamide as a common antibiotic. The EO system degraded completely sulfanilamide and generated 150 µM of H2O2 and 8 mg/L of DO even at 10 mA. In other words, EO system can directly oxidize the sulfanilamide and produce oxygen species. The pyrite system produced 204 and 24 µM of hydroxyl radicals at pH 3 under oxic and anoxic conditions, respectively, and 118 and 20 µM at pH 7. Pyrite oxidation can generate more reactive species in the presence of oxygen. The combined system enhanced the oxidation-rate constant to 1.5 times (from 0.2561 to 0.3502 h-1). The additional supply of oxygen showed a higher oxidation rate to 1.5 and 1.3 times higher than single EO or pyrite oxidation, respectively. As a result, the co-presence of pyrite and oxygen shows a synergistic effect on the oxidation of the organic pollutant. Our results suggest that electrochemical generation of the oxygen species in the presence of pyrite is a promising technique to oxidize organic pollutants in groundwater.

Desorption technologies for remediation of cesium-contaminated soils: a short review.

This review summarizes the mechanisms for desorbing and extracting cesium (Cs+) from clay minerals and soil. Most techniques use ion exchange with acids, cations, polymers, and surfactants. Some improve desorption of Cs+ from clay minerals, while surfactants and polymers expand the interlayer. Mixtures of acids/polymers, acids/surfactants, cations/polymers, and cations/surfactants are therefore more effective agents for desorption of Cs+ from clay minerals. Hydrothermal treatment plays a role similar to that of polymers and surfactants in expanding the interlayer of clay minerals. The primary desorption mechanism expands the interlayer and desorbs Cs+, but multiple sequential extractions based on these techniques can more effectively desorb Cs+ from clay minerals and field-contaminated soils. Desorption techniques for Cs+ based on multiple sequential extractions can reportedly achieve an efficiency greater than 90%, and such approaches are likely to be important technologies for remediation of Cs+-contaminated soils and industrial accident sites, as well as the dismantling of nuclear power plants.

Dual radicals-enhanced wet chemical oxidation of non-biodegradable chemicals.

Total organic carbon (TOC) has been suggested and utilized as an index of organic matter in aqueous phases. The overall performance of TOC is highly dependent on the method of oxidation of organic matter to carbon dioxide, such as high-temperature combustion (HTC) and wet chemical oxidation (WCO). HTC requires more energy and maintenance cost, it is a major barrier to the field application. In contrast, WCO is more suitable for the application of on-line monitoring systems due to requiring lower energy and easy maintenance. However, WCO shows lower oxidation than HTC, thus, oxidation performance should be improved for the application to the field. In this study, a dual radical system (DRS), including sulfate and hydroxyl radicals, was proposed to enhance oxidation ability. The DRS uses alkaline pH and persulfate to generate sulfate radicals, which have been used to activate hydroxyl radicals and oxidize organic matter. The oxidation mechanism for the DRS has been verified using model chemicals with different reaction rate constants. The applicability of the DRS has been confirmed using authentic wastewater with a high concentration of chloride. In this study, the DRS showed similar performance compared to the HTC within 10 % error range. The DRS shows similar oxidation performance with HTC even at a high concentration of chloride. DRS did not show interference by the presence of chloride up to 30,000 mg/L of chloride. Results of this study indicate that the DRS can enhance overall oxidation performance compared to the conventional WCO system.

Role of carbon fiber electrodes and carbonate electrolytes in electrochemical phenol oxidation.

In-situ chemical oxidation (ISCO) requires an injection of oxidants into a contaminated site. However, the oxidants decompose and react with contaminants during transport to the contaminated region, which causes oxidant over-consumption. In-situ oxidant generation can solve this problem, and electrochemical methods can be applied to achieve this. Electrochemical oxidation is highly dependent on electrode material type. In this study, we evaluated graphite and carbon fiber as candidates for electrochemical oxidant generation and phenol as the model compound. The carbon fiber anode oxidized the phenol more effectively than graphite, with removal proportional to the applied current. Carbonate electrolytes were more effective at oxidizing phenols than sulfate electrolytes. The faster carbon fiber anode phenol oxidation is due to its large surface area. Carbonate radicals in the carbonate electrolyte contribute to phenol oxidation as well as further intermediate oxidation. The carbon fiber cathode was not an effective phenol oxidizer even though it generated more hydrogen peroxide. This is because there was no catalyst to transform the hydrogen peroxide into hydroxyl radicals. Results indicate that electrochemical oxidation using carbon fiber is an effective method for treating phenol found in groundwater with high concentrations of (bi)carbonate.

Bifunctional iron-modified graphitic carbon nitride (g-C3N4) for simultaneous oxidation and adsorption of arsenic.

Iron-modified graphitic carbon nitride (FG materials) was prepared through a simple and cost-effective method using iron oxide and melamine to achieve simultaneous oxidation and adsorption of arsenic. We hypothesized that graphitic carbon nitride oxidizes As(III) to As(V) under light irradiation, and the converted As(V) is adsorbed by the amorphous iron phase on FG materials. FG materials were characterized by X-ray diffraction, Fourier transform infrared spectra, field-emission scanning electron microscopy, specific surface area, ultraviolet-visible light spectroscopy, photoluminescence, and X-ray photoelectron spectroscopy. As(III) was efficiently transformed to As(V) due to the photocatalytic-oxidation ability of graphic carbon nitride under visible and UV light irradiation, the oxidized As(V) was adsorbed by the amorphous iron phases, and As species were removed from the system. The removal efficiency of As(III) decreased from 50%, 41%, and 33% under UV light, visible light and dark, respectively. FG materials exhibited the photocatalytic-oxidation ability and adsorption capacity, and a synergistic effect was observed between graphitic carbon nitride and iron oxide. Removal of As can be achieved even under visible light, confirming the field applicability of low-cost FG materials.

Simultaneous oxidation and adsorption of arsenic by one-step fabrication of alum sludge and graphitic carbon nitride (g-C3N4).

The oxidation of trivalent arsenic (As(III)) to pentavalent arsenic (As(V)) is a common pretreatment to remove As(III) from the aqueous phase. The graphitic carbon nitride as a photocatalyst can transform As(III) to As(V), but the photocatalyst does not adsorb any species of arsenic. In this study, a new composite material to achieve the simultaneous oxidation and adsorption of arsenic was synthesized by co-pyrolyzing alum sludge and melamine. It was hypothesized that graphitic carbon nitride derived from melamine oxidizes As(III) to As(V) and pyrolyzed alum sludge provides strong adsorption sites for the oxidized As(V). The composites were characterized by X-ray diffraction, Brunauer-Emmett-Teller(BET) surface, scanning electron microscope, and X-ray photoelectron spectrometer. The composite material effectively converted As(III) to As(V) under the light, and the total arsenic concentration decreased in the aqueous phase via the adsorption of As(V). Speciation analysis of arsenic on the composite showed that both As(III) and As(V) species were present on the surface of adsorbent, from which desorption by mixing with deionized water was difficult. This new and green composite material can oxidize As(III) and adsorb arsenic simultaneously under the light, which can be used to treat arsenic-containing water.