Removal Of Sulfamethazine Research Articles

Comparison of Four Tourmalines for PS Activation to Degrade Sulfamethazine: Efficiency, Kinetics and Mechanisms.

Four types of tourmalines (TMs, S1, S2, S3 and S4) for activating persulfate (PS) to degrade sulfamethazine (SMT) were compared to find the most efficient catalyst. The four TMs were mesoporous materials with abundant functional groups, but were different in terms of size, composition, specific surface area, contact angle, and zero potential point. The removal of SMT in S1, S2, S3 and S4 systems with PS at the optimum reaction conditions ([SMT]0 = 5 mg/L, [PS]0 = 4 mM, [TM]0 = 5 g/L, pH0 = 5, and T = 25 °C) were 99.0%, 25.5%, 26.0%, and 51.0%, respectively, which might be related to the metal content of TM. Although the degradation of SMT in the S1/PS/SMT system was not dominated by SO4•− and •OH, the radicals contributed to the SMT removal in the S2, S3, and S4 systems. 1O2 and holes both contributed to the degradation of SMT in the four systems. The metal at the X position might be related to the generation of 1O2 and holes, while Fe of TM was mainly related to the generation of free radicals, such as SO4•−. Electrochemical impedance spectroscopy tests confirmed that the separation of electrons and holes on the TM surface could be promoted by adding PS and SMT. S1 presented a higher electron-transfer rate than the other three TMs. The PS activation by TM with a high metal content at the X position provided an efficient and low-consumption treatment for antibiotic refractory wastewater.

Degradation of sulfamethazine in water by sulfite activated with zero-valent Fe-Cu bimetallic nanoparticles

In this work, zero-valent Fe-Cu bimetallic nanoparticles were synthesized using a facile method, and applied to activate sulfite for the degradation of sulfamethazine (SMT) from the aqueous solution. The key factors influencing SMT degradation were investigated, namely the theoretical loading of Cu, Fe-Cu catalyst dosage, sulfite concentration and initial solution pH. The experimental results showed that the Fe-Cu/sulfite system exhibited a much better performance in SMT degradation than the bare Fe0/sulfite system. The mechanism and possible degradation pathway of SMT in Fe-Cu/sulfite system were revealed. The reactive radicals that played a dominant role in the SMT degradation process were •OH and SO4•-, while the loading of Cu induced the synergistic effect between Fe and Cu. The redox cycle between Cu(I)/Cu(II) remarkably contributed to the conversion of Fe(III) to Fe(II), greatly enhancing the catalytic performance of Fe-Cu bimetal. In real groundwater applications, the Fe-Cu/sulfite system also exhibited satisfactory SMT degradation. The 30-day aging tests of Fe-Cu particles demonstrated that the aging of catalyst was not obviously affecting the removal of SMT. Furthermore, the reusability of catalyst was evidenced by the recycling experiments. This study provides a promising application of bimetal activated sulfite for enhanced contaminant degradation in groundwater.

Novel sphere-like copper bismuth oxide fabricated via ethylene glycol-introduced solvothermal method with improved adsorptive and photocatalytic performance in sulfamethazine removal.

In this research, ethylene glycol-introduced solvothermal method was employed to fabricate a novel sphere-like CuBi2O4 material to improve the adsorptive and photocatalytic performance of conventional CuBi2O4. A series of characterization has been applied to investigate properties of the obtained CuBi2O4 (CBO-EG3). Compared with conventional rod-like CuBi2O4 (CBO), the synthesized sphere-like CBO-EG3 exhibited rough surface, larger specific surface area, and more effective separation of photo-generated carriers, which overcome main shortcomings of CuBi2O4. The removal efficiency of typical antibiotic sulfamethazine (SMZ) reached almost 100% under the optimal experimental conditions. About 70% of SMZ could be adsorbed in 180-min dark reaction, with residual being photodegraded in 30min. CBO-EG3 showed much higher photocatalytic efficiency than pure CBO, attributing to its highly effective photo-induced electron and hole separation. Meanwhile, substantial adsorption of pollutant on CBO-EG3 contributed vastly to removal of SMZ, photo-generated electrons and holes inclined to react with adsorbed SMZ directly, and photocatalytic process was mainly led by non-radical reaction. Elimination of SMZ in actual water samples and recycling experiment were also performed to evaluate CBO-EG3's practical application potential. This study delivered a method to promote CuBi2O4's adsorptive and photocatalytic ability, which could expand the application of CuBi2O4 in wastewater treatment.

Activation of peroxymonosulfate by a floating oxygen vacancies - CuFe2O4 photocatalyst under visible light for efficient degradation of sulfamethazine

In this study, expanded perlite supported oxygen vacancies-CuFe2O4 (OVs-CFEp) was synthesized via a simple method and utilized as floating catalyst to activate peroxymonosulfate (PMS) for the removal of sulfamethazine (SMT) under visible light irradiation. OVs-CFEp/Vis/PMS synergy presents much superior performance than that of OVs-CFEp/Vis system and OVs-CFEp/PMS system. PMS was efficiently activated by OVs-CFEp at a wide range of pH values, while the degrading rate of SMT was up to 95% in OVs-CFEp/Vis/PMS system. Oxygen vacancies and ·O2− accelerated the conversion of Fe(III)/Fe(II) and Cu(I)/Cu(II). The combination of the floating loader boosted light absorption capacity and sufficiently prevented metal ions leaching, which was all beneficial to enhance catalytic performance and recyclability. Besides, the reactive oxygen species were investigated systematically, proving that visible light and OVs-CFEp could activate PMS to produce ·SO4−, ·OH, O2·−, and 1O2 reactive species. Furthermore, based on intermediates identification and Density Functional Theory (DFT) calculation, three types and seven main degradation pathways involving cleavage of bond, SMT molecular rearrangement, and hydroxylation reaction were proposed. So this high photo-absorbing catalyst coupling with advanced oxidation progress was promising for extensive environmental remediation.

High yield M-BTC type MOFs as precursors to prepare N-doped carbon as peroxymonosulfate activator for removing sulfamethazine: The formation mechanism of surface-bound SO4•- on Co-Nx site

M-BTCs (M = Fe, Co and Mn)/melamine were used to prepare N-doped carbon materials, and their performances as activator of peroxymonosulfate (PMS) for sulfamethazine (SMZ) removal were compared. M-BTC type metal-organic frameworks (MOFs) were synthesized under room temperature, with their yield about 7.5 times of ZIF-67 which is the most used MOFs to prepare N-doped carbon materials as the catalyst of persulfate-based advanced oxidation processes. Co-BTC/melamine derived N-doped carbon materials (Co-BTC/5MNC) performed the best, even better than that of ZIF-67 derived N-doped carbon materials. Initial pH (3–9), 0–10 mM inorganic anions (Cl−, NO3−, HCO3− and H2PO42−) and humic acid (5 and 10 mg/L) had no obvious inhibition on SMZ removal with Co-BTC/5MNC as catalyst. The results of both X-ray photoelectron spectroscopy and density functional theory (DFT) calculations indicated that N-coordinated cobalt single atom site (Co−Nx) was the possible active site of Co-BTC/5MNC. Importantly, surface-bound SO4•- was identified as the dominant reactive oxygen species for SMZ removal. The SO4•- generated through the charge transfer between PMS and catalyst, and was tightly adsorbed on Co-Nx site.

Aminopolycarboxylic acids modified oxygen reduction by zero valent iron: Proton-coupled electron transfer, role of iron ion and reactive oxidant generation

The oxygen reduction reaction (ORR) activated by Fe0 in the presence of three aminopolycarboxylic acids (CAs), i.e. nitrilotriacetic acid (NTA), ethylenediamine-N,N′-disuccinic acid (EDDS) and ethylenediaminetetraacetic acid (EDTA), for the degradation of sulfamethazine (SMT) was investigated. At optimum conditions, Fe0/EDDS/O2, Fe0/EDTA/O2 and Fe0/NTA/O2 systems presented SMT removal of 58.2%, 75.3% and 93.8%, respectively, being much higher than that in the Fe0/O2 system (1.36%). The generation of surface-bound Fe2+ (Fe2+) and dissolved iron ion was enhanced by CAs. ORR through a two-electron transfer pathway was mainly responsible for H2O2 generation in NTA and EDTA systems, while a single-electron ORR was the major source for producing H2O2 in EDDS system. •OH produced by the homogeneous reaction of Fe2+ and H2O2 was the main species for SMT degradation. Fe0/EDDS/O2 produced more 1O2 than Fe0/EDTA/O2 and Fe0/NTA/O2; however, the radical contributed negligibly to SMT removal. The caging effect of CAs might be a major factor influencing the reaction rate of Fe2+ and O2. CAs provided protons to accelerate the electron transfer, the production of Fe2+ and thus the contaminant removal. This study is of great significance for revealing ORR mechanisms in the Fe0-chelate system.

Degradation of sulfamethazine by vacuum ultraviolet-activated sulfate radical-advanced oxidation: efficacy, mechanism and influences of water constituents

• VUV/PMS enhanced the SMT removal in greywater than UV/PMS. • HO• was the most effective radical for SMT degradation, followed by SO 4 • − . • VUV/PMS enhanced the oxidative degradation rather than photolysis. • SMT degradation pathways and intermediates toxicology for VUV(UV)/PMS were analysed. In-situ collection, purification and reuse of indoor greywater of public buildings or household is an effective way to save water resources. Refractory organic micropollutants in greywater, such as antibiotic sulfamethazine (SMT), can be potentially removed by sulfate radical-advanced oxidation process (SR-AOP) in the presence of peroxymonosulfate (PMS) or peroxydisulfate. Herein, vacuum ultraviolet (VUV) with irradiation at 185 nm and 254 nm activating PMS was systematically investigated in terms of degradation efficacy and influences of water constituents, and the contribution of photolysis and radical oxidative species was determined. We show that SMT removal efficiency and PMS photolysis efficiency of VUV/PMS were 2.2-fold and 1.45-fold compared to UV/PMS, respectively, and VUV/PMS reached a higher mineralization. The main active radicals of VUV/PMS were HO•, SO 4 •− , and •O 2 − . Compared to UV/PMS, VUV/PMS resulted in a higher proportion of oxidative degradation and a lower proportion of photolysis. Higher SMT concentrations competed for absorption of VUV or UV-generated photons with H 2 O and PMS molecules, resulting in a less efficient reaction. VUV/PMS was more efficient at lower initial SMT concentrations and had an optimal pH of 5. The presence of SO 4 2− slightly accelerated degradation performance while HCO 3 − and NO 3 − inhibited both processes; the inhibitory effect of HCO 3 − and NO 3 − on VUV/PMS are more significant than on UV/PMS. In contrast, the presence of Cl − had no significant effect on each process. In total, 13 intermediates of SMT were identified and four degradation pathways were proposed. VUV/PMS had an advantage over UV/PMS in removing the produced harmful and toxic intermediates. Furthermore, VUV/PMS could remove SMT from real water matrix more effectively than UV/PMS. Generally, the results demonstrate the potential of VUV to displace UV for more effective in-situ treatment of indoor greywater.

A flow-through UV/electro-chlorine process for cost-effective and multifunctional purification of marine aquaculture wastewater

This study validated the feasibility of the simultaneous removal of antibiotics such as sulfamethazine and other pollutants including ammonia nitrogen, nitrate nitrogen and phosphorus, as well as disinfection in marine aquaculture wastewater by using a flow-through ultraviolet/electro-chlorine (EO+UV) process, comparing the removal performance and energy consumption with that by separate EO and UV process. Due to the co-action of multiple radicals and free chlorine, the removal of sulfamethazine and ammonia nitrogen by using EO+UV process was much higher than that by using EO and UV. This process could achieve complete inactivation of bacteria and removal of sulfamethazine under optimal conditions of 10 mA (1.4 mA/cm2), flow rate 15 mL/min and pH 8.0. It also exhibited an effective removal of other antibiotics (norfloxacin, chloramphenicol and cephalexin). During treatment, 5.0–87.0 mg/L free chlorine was generated by EO process at current of 10–50 mA (1.4–7.1 mA/cm2), and it was further converted into a variety of radicals under UV irradiation such as hydroxyl (4.95–9.45 μmol/L) and chlorine radical, which greatly improved the performance and reduced the energy consumption to only 19.0 kWh/kg, far lower than other processes. This flow-through EO+UV process had great practical application prospects for the comprehensive removal of multiple pollutants especially antibiotics and sterilization from marine aquaculture wastewater.

Investigation on the structure-performance of phthalic acid carboxyl position and carbon nitride towards efficient photocatalytic degradation of organic pollutants

Polymeric carbon nitride as photocatalysts to address environmental issues attract broad interest. Anchoring aromatic ring on CN surface can improve its charge pair separation, but the effect of functional group position of aromatic ring on its performance is ignored. Herein, we used three isomers of phthalic acid (phthalic acid, isophthalic acid and terephthalic acid) and urea to synthesize modified carbon nitride as a photocatalyst to remove sulfamethazine (SMZ). The phthalic acid may act as group modification and enhanced the absorption of longer wavelengths of carbon nitride, while part of isophthalic acid and terephthalic acid may enter the framework of carbon nitride as benzene ring and the others may act as the amorphous carbon in carbon nitride. Consequently, the phthalic acid modified carbon nitride (PA-CN) exhibited the optimal degradation performance for SMZ removal (0.0737 min−1). It was further revealed that the O2− and h+ played the significant role in the photocatalytic process. This study reveals the effect of the position of organic acid functional groups on the performance of carbon nitride, and points out that PA-CN can be applied to the purification of wastewater containing refractory pollutants.

Enhanced activation of sulfite by a mixture of zero-valent Fe-Mn bimetallic nanoparticles and biochar for degradation of sulfamethazine in water

Due to the inherent disadvantages of homogeneous transition metal-activated sulfite system, such as narrow pH range, slow Fe3+/Fe2+ circulation and low electron transfer efficiency, the heterogeneous system of zero-valent Fe-Mn bimetallic nanoparticles (ZVFMB) physically mixed with biochar (BC) to activate sulfite(S(IV)) was developed to improve the removal of sulfamethazine (SMT). The results showed that the heterogeneous ZVFMB-BC/S(IV) system could rapidly degrade 92% of SMT within 15 min, because of the formation of a large number of active radicals, mainly hydroxyl radicals (62.2%). Through in-depth discussion, we found that due to the obvious defect structure (ID/IG = 2.05) and abundant phenolic hydroxyl groups on the surface of biochar, biochar was fully qualified for the roles of electron shuttle and electron donor, which were verified by various characterization methods such as FTIR, Raman and linear sweep voltammetry (LSV). Startlingly, it was worth mentioning that biochar can be activated in situ in the oxidation process to form micropores and increase the surface area and pore volume, which facilitated the rapid degradation of SMT. Moreover, this system also shows excellent performance in other water bodies, such as simulated groundwater under neutral or weak acidic conditions and water bodies with other pollutants (e.g., SBD, CBZ, ATZ). All in all, compared to the traditional Fe/Mn ions activated sulfite system, this system has a wide range of pH tolerance, high electron transfer efficiency and excellent degradation rate, showing great potential for application in the degradation of organic pollutants.

Sulfamethazine removal by peracetic acid activation with sulfide-modified zero-valent iron: Efficiency, the role of sulfur species, and mechanisms

Sulfide-modified zero-valent iron (S-Fe0) has been regarded as a promising method to enhance the catalytic activity of Fe0. Therefore, peracetic acid (PAA) firstly activated by S-Fe0 was conducted to remove sulfamethazine (SMT) in this study. Only 13.1% SMT could be removed within 60 min in Fe0/PAA system while 86.5% SMT could be removed within 60 min in S-Fe0/PAA system at condition of [PAA] = 100 μΜ, [S-Fe0] = 20 mg/L, [SMT] = 5 mg/L, pH = 4.0. The effect of S/Fe ratio, S-Fe0 dosage, PAA concentration and initial pH on SMT removal were investigated. The characterization of S-Fe0 such as SEM, XPS, contact angle and Tafel confirmed that the formation of sulfur species on Fe0 surface could enhance the catalytic performance of Fe0. S2− played the major role and SO32- played the minor role in accelerating the conversion of Fe3+ to Fe2+. •OH and R-O• exhibited 67.1% and 32.5% contribution for SMT removal in S-Fe0/PAA system, respectively. The possible degradation pathway of SMT was also proposed. Cl− and HCO3– had a negligible adverse effect on SMT removal in S-Fe0/PAA system indicating the good adaptability of inorganic ions. In addition, S-Fe0/PAA system had the good recycle ability of S-Fe0 and showed a better performance in removing SMT in the natural fresh water. Therefore, this study notably showed the potential applicability of S-Fe0/PAA system in degrading SMT in natural fresh water.

S-doped MIL-53 as efficient heterogeneous electro-Fenton catalyst for degradation of sulfamethazine at circumneutral pH

The reduced S-modified MIL-53(Fe) was prepared by sulfurizing MIL-53(Fe) at low temperature, which was an efficient electro-Fenton catalyst at wide pH range (3–9) for sulfamethazine (SMT) degradation. The best temperature and MIL-53(Fe)/S ratio were 350 °C and 1:2, at which the BET surface area was much enlarged. The MIL-53(Fe) surface was etched by S to many 2D nanosheets with the thickness of ~50 nm, while S2–2 replaced OH- to coordinate with Fe2+ and increased the Fe2+ content, which improved the catalytic performance. Even at initial pH of 7.0, the SMT removal was 95.8%, and the rate constant (k) in the Hetero-EF process was 16-folds of that in the Homo-EF process. The turnover frequency (TOFd) value of MIL-53(Fe)/S(1:2)−350 was 0.48 L g−1 min−1, which was 6.8 times that of commercial FeS2. The S2–2in catalyst adjusted the pH superfast, and promoted the generation of Fe2+ and thus efficiently activating H2O2 to form surface ·OH, which was verified to be the main radical by EPR and radical scavenger experiments. This catalyst showed promising prospect for environmental application and could be regenerated by sulfidation method. S-doped MIL-53(Fe) was an excellent pH regulator, thus promoting promising application in Hetero-EF processes.

Ferrate (VI) as efficient oxidant for elimination of sulfamethazine in aqueous wastes: Real matrix implications

The presence of antibiotics in aquatic environments has become a serious concern since they develop the antibiotic/multi-drug-resistant bacteria which further affect to living beings. The study intended to assess the freshly synthesized ferrate (VI) in the degradation of an important emerging micro-pollutant i.e., sulfamethazine (SMZ). Moreover, the real matrix implications are extensively conducted for implication of ferrate (VI) technology as safer and viable options. Batch reactor studies enabled the molar ratio of ferrate (VI) to sulfamethazine is 2:1 with overall rate constant 6,128 mM-2.min-1. Percentage elimination of sulfamethazine was observed Ca. 80% at initial sulfamethazine concentration 0.02 mM and ferrate (VI) dose 0.1 mM. Presence of several co-ions NaCl, Na2HPO4, NaNO3, oxalic acid and NaNO2 showed insignificant effect on elimination of sulfamethazine; whereas the efficiency of ferrate (VI) was lowered due to glycine and EDTA. Mineralization of sulfamethazine is significantly increased at lower pH value (pH 5.0). Further, the removal of sulfamethazine in the real water matrix showed that the elimination efficiency of sulfamethazine is almost unaffected as compared to the distilled water treatment. This implied that ferrate (VI) is a viable and greener option for treatment of emerging water pollutants to enhance the efficiency of existing wastewater treatment plants.

Removal of sulfamethazine using peracetic acid activated by Fe0 and UV: Efficiency and mechanism study

Peracetic acid (PAA) was successfully activated by UV and Fe0 to degrade sulfamethazine (SMT) in this study. UV/Fe0/PAA system not only could enhance SMT removal efficiency but also could reduce the energy consumption in comparison with UV, Fe0/PAA and UV/PAA systems. The RO• radical was the main radical for the degradation of SMT in UV/Fe0/PAA system and photolysis, •OH and R-O• exhibited 15.6%, 17.6% and 66.8% contribution for SMT degradation, respectively. Fourier transform infrared spectroscopy (FTIR), Scanning Electron Microscope (SEM), and X-ray photoelectron spectroscopy (XPS) were conducted to investigate the characterization of Fe0 after reaction in UV/Fe0/PAA system. The possible SMT degradation pathway was also proposed. Affecting factors such as Fe0 dosage (0–0.2 g L−1), PAA concentration (0–200 μM) and initial pH (3–9) were also studied. Cl−, NO3-, SO42- and HCO3- had a negligible adverse effect on SMT removal in this system indicating the good adaptability to inorganic ions. In addition, UV/Fe0/PAA system had the good recycle ability of Fe0 and showed a good performance in removing antibiotic in the nature fresh water. Therefore, this study notably improved the knowledge of PAA activated by Fe0 and UV and showed the potential applicability of UV/Fe0/PAA system in degrading antibiotics in nature fresh water.

MOF-derived Cu0/C activation of molecular oxygen for efficient degradation of sulfamethazine

Zero-valent copper (ZVC) has shown potential as an oxygen activator for the degradation of organic pollutants from aqueous solution. Nevertheless, the high leaching of copper ions and the demand for acidic condition limited its application. In this study, a novel mesoporous carbon hybrid loaded zero-valent copper (Cu0/C) was successfully synthesized from Cu-based metal–organic framework (Cu3(BTC)2) through a pyrolysis method and applied to efficiently degrade sulfamethazine (SMT) at neutral pH under aeration condition. The performance of Cu0/C composite for the activation of molecular oxygen was evaluated based on the effect of different reaction parameters, such as, initial SMT concentration, initial pH, activator dosage and reaction temperature. The results showed a high efficiency for SMT removal over a broad pH range (3.0–7.0). Moreover, the Cu0/C composite exhibited excellent stability and reusability for SMT degradation, and a 96.7% SMT removal and a 68.8% total organic carbon (TOC) conversion were achieved at pH 5.8 after continuous three cycles. Combined with the determination results of reactive oxidizing species and physical-chemical characterization, cupryl species (Cu3+) rather than OH produced by the reaction of the in-situ generated H2O2 with Cu+ were the major reactive species. Additionally, the possible reaction mechanism of Cu0/C activated oxygen was tentatively proposed.

Phototransformation of Graphene Oxide on the Removal of Sulfamethazine in a Water Environment.

Graphene oxide (GO) is widely used in various fields and has raised concerns regarding its potential environmental fate and effect. However, there are few studies on its influence on coexisting pollutants. In this study, the phototransformation of GO and coexisting sulfamethazine (SMZ) under UV irradiation was investigated, with a focus on the role of reactive oxygen species. The results demonstrated that GO promoted the degradation of SMZ under UV irradiation. The higher the concentration of GO, the higher the degradation rate of SMZ, and the faster the first-order reaction rate. Two main radicals, ∙OH and 1O2, both contributed greatly in terms of regulating the removal of SMZ. Cl−, SO42−, and pH mainly promoted SMZ degradation by increasing the generation of ∙OH, while humic acid inhibited SMZ degradation due to the reduction of ∙OH. Moreover, after UV illumination, the GO suspension changed from light yellow to dark brown with increasing absorbance at a wavelength of 225 nm. Raman spectra revealed that the ID/IG ratio slightly decreased, indicating that some of the functional groups on the surface of GO were removed under low-intensity UV illumination. This study revealed that GO plays important roles in the photochemical transformation of environmental pollutants, which is helpful for understanding the environmental behaviors and risks of nanoparticles in aquatic environments.

Tuning band structure of graphitic carbon nitride for efficient degradation of sulfamethazine: Atmospheric condition and theoretical calculation

Numerous approaches have been used to modify graphitic carbon nitride (g-C 3 N 4 ) for improving its photocatalytic activity. In this study, we demonstrated a facial post-calcination method for modified graphitic carbon nitride (g-C 3 N 4 -Ar/Air) to direct tuning band structure, i.e. , bandgap and positions of conduction band (CB)/valence band (VB), through the control of atmospheric condition without involving any additional elements or metals or semiconductors. The synthesized g-C 3 N 4 -Ar/Air could efficiently degrade sulfamethazine (SMT) under simulated solar light, i.e. , 99.0% removal of SMT with rate constant k 1 = 2.696 h −1 within 1.5 h (4.9 times than pristine g-C 3 N 4 ). Material characterizations indicated that the damaged/partial-collapsed structure and decreased nanosheet-interlayer distance for g-C 3 N 4 -Ar/Air resulted in the shift of band structure due to the denser stacking of pristine g-C 3 N 4 through oxidative exfoliation and planarization by air calcination. In addition, the bandgap of g-C 3 N 4 -Ar/Air was slightly shrunk from 2.82 eV (pristine g-C 3 N 4 ) to 2.79 eV, and the CB was significantly upshifted from −0.44 eV (pristine g-C 3 N 4 ) to −0.81 eV, suggesting the powerful ability for donating the electrons for O 2 to form • O 2 − . Fukui index ( f – ) based on theoretical calculation indicated that the sites of SMT molecule with high values, i.e. , N9, C4 and C6, preferred to be attacked by • O 2 − and • OH, which is confirmed by the intermediates’ analysis. The tuning method for graphitic carbon nitride provides a simple approach to regulate the charge carrier lifetime then facilitate the utilization efficiency of solar light, which exhibits great potential in efficient removal of emerging organic contaminants from wastewater. Modified graphitic carbon nitride (g-C3N4-Ar/Air) was synthesized via a facial post-calcination method and exhibited efficiently photocatalytic activity for SMT removal due to the tune of band structure.

Adsorption and catalytic degradation of organic contaminants by biochar: Overlooked role of biochar’s particle size

Biochar (BC) is considered as a promising adsorbent and/or catalyst for the removal of organic contaminants. However, the relationship between the particle size of BC and its adsorption/catalysis performance is largely unclear. We therefore investigated the influence of particle size on the performance of BC pyrolyzed at 300–900 °C in trichloroethylene (TCE) adsorption and persulfate (PS) activation for sulfamethazine (SMT) degradation. The results showed that high-temperature pyrolyzed BC (BC900) presented superior adsorption capacity for TCE and excellent catalytic activity for PS activation to degrade SMT. Compared to 150–250 µm, 75–150 µm and pristine BC900, 0–75 µm BC900 showed the highest TCE adsorption efficiency, which increased by 19.5–62.3%. Similarly, SMT removal by BC900/PS systems also increased from 24.2% to 98.3% with decreasing BC particle size. However, the catalytic activity of BC after grinding was not significantly improved as expected, indicating the properties of biochar was not only controlled by size effect. Characterization measurements proved that small-sized BC tended to have larger specific surface area, more micropores, higher conductivity, rich graphitic domains and surface redox-active functional groups, thus resulting in an enhanced adsorption and catalytic ability of BC.

Optimization of electrochemical activation of persulfate by BDD electrodes for rapid removal of sulfamethazine

Boron-doped diamond electrodes have been employed for the removal of sulfamethazine (SMZ) from water by electrochemical activation of persulfate (EO/BDD-PS). A set of experiments with a central composite design (CCD) was conducted to optimize the operating parameters such as persulfate dose, solution pH, and current density by response surface methodology (RSM). The experimental results indicated a rapid degradation of SMZ even at high initial concentrations. For instance, complete degradation of 50 mg L−1 of SMZ was attained after 15 min at the optimum operating conditions (persulfate loading = 0.40 g L−1, pH = 4, and current density = 21 mA cm−2). The oxidation mechanism of EO/BDD-PS process was studied based on the reactive oxidant species (ROS) revealing that both (OH) and ▪ contributed to the degradation of SMZ in the EO/BDD-PS system. Furthermore, the oxidation pathway has been proposed by the suspect screening and tandem mass spectrometry analysis. The performance of EO/BDD-PS showed faster SMZ degradation than electro-Fenton and anodic oxidation processes using the same BDD electrochemical reactor under the same conditions. Furthermore, we provided a cost estimation study revealing that a full-scale application of the EO/BDD-PS system for the treatment of similar contaminated water costs about $2.23 m-3.

Fabrication of novel FeS2 NWs/Ti3C2 cathode for Photo-Electro-Fenton degradation of sulfamethazine

A novel pyrite nanowires (FeS2 NWs)/Ti3C2 composite with 1D-2D hybrid was developed as the cathode for efficient removal of sulfamethazine (SMT) through Photo-Electro-Fenton (PEF) mechanism. FeS2 NWs demonstrated the best PEF performance among different iron sulfide crystalline phases (pyrite, pyrrhotite and mackinawite). The FeS2 NWs/Ti3C2 (FeS2:Ti3C2 = 2:1) cathode exhibited the highest PEF degradation efficiency of 97.6% for SMT (10 mg/L) within 80 min. Diffuse reflection spectra (DRS) indicated the superior light absorption of FeS2 due to the narrow band gap, and Ti3C2 further improved the light utilization of the composite by separating the photogenerated charge carriers and broadening the light absorption region. Photocurrent and electrochemical impedance spectroscopy (EIS) demonstrated the low resistance and rapid charge transfer of FeS2 NWs. Meanwhile, the conductivity of the composite was enhanced by the introduction of Ti3C2, which was ascribed to the promoted electron migration and prolonged carrier lifetime. The FeS2 NWs/Ti3C2 cathode showed excellent recyclability of preserving 92.8% of initial performance after five cycles due to the rapid Fe3+/Fe2+ cycling. Excellent selectivity was also revealed for the FeS2 NWs/Ti3C2 cathode toward two-electron oxygen reduction reaction (ORR) pathway (n = 2.34), ensuring constant H2O2 generation. The radical scavenging experiment also demonstrated that the main oxidant in PEF system was OH. This work paves the way for the novel design and synthesis of highly efficient PEF cathodes.