Propylene glycol-mixed steam enhanced extraction for an efficient and sustainable remediation of PAHs-contaminated soil.

An innovative thermal desorption method, propylene glycol (PG)-mixed steam enhanced extraction, is proposed for a highly efficient remediation of polycyclic aromatic hydrocarbons (PAHs)-contaminated soil. It is found that injecting PG-mixed steam into soil column could obtain > 99% removal efficiencies of PAHs either for the pyrene-spiked soil, or for the contaminated field soil with high-molecular-weight PAHs. PG is a safe and low-cost dihydric alcohol with a boiling point higher than water. When the PG-mixed steam penetrated the contaminated soil, the PG vapor preferentially condensed to form a hot liquid with concentrated PG (e.g., from 30 wt% PG in gas phase to 90 wt% PG in the liquid phase), which would significantly solubilize the PAHs and enhance their desorption from soils. The results also revealed that the effluents derived from the PG-mixed steam could be purified by removing the desorbed PAHs using a simple coagulation treatment, and the recovered PG solution could be reused. The plant assay using wheat seeds showed that the remediated soil had a good regreening potential. Our results demonstrate that PG-mixed steam injection is a promising thermal desorption method for an efficient and sustainable remediation of PAHs-contaminated soil.

Highly Selective Reduction of Nitrate by Zero-Valent Aluminum (ZVAI) Ball-Milled Materials at Circumneutral pH: Important Role of Microgalvanic Cells for Depassivation of ZVAl and N2-Selectivity.

The passivation of zero-valent aluminum (ZVAl) limits its application in environmental remediation. Herein, a ternary composite material Al-Fe-AC is synthesized via a ball-milling treatment on a mixture of Al0, Fe0, and activated carbon (AC) powders. The results show that the as-prepared micronsized Al-Fe-AC powder could achieve highly efficient nitrate removal and a nitrogen (N2)-selectivity of >75%. The mechanism study reveals that, in the initial stage, numerous Al//AC and Fe//AC microgalvanic cells in the Al-Fe-AC material could lead to a local alkaline environment in the vicinity of the AC cathodes. The local alkalinity depassivated the Al0 component and enabled its continuous dissolution in the subsequent second stage of reaction. The functioning of the AC cathode of the Al//AC microgalvanic cell is revealed as the primary reason accounting for the highly selective reduction of nitrate. The investigation on the mass ratio of raw materials manifested that an Al/Fe/AC mass ratio of 1:1:5 or 1:3:5 was preferable. The test in simulated groundwater suggested that the as-prepared Al-Fe-AC powder could be injected into aquifers to achieve a highly selective reduction of nitrate to nitrogen. This study provides a feasible method to develop high-performance ZVAl-based remedial materials that could work in a wider pH range.

Efficient activation of peroxodisulfate by novel bionic iron-encapsulated biochar: The key roles of electron transfer pathway and reactive oxygen species evolution.

In this study, a novel iron-encapsulated biochar (Fe@BC) was prepared using the biomass cultivated with an iron-containing solution. The iron in Fe@BC showed the phase change from Fe3O4 to α-Fe, and to CFe15.1, with the increase of pyrolysis temperature (500-900 °C), and a graphene shell formed on the surface of Fe@BC. In addition, the signals assigned to the π-π* shake up, pyridinic N, graphitic N, and defects of Fe@BC were found to be stronger as the pyrolysis temperature increased. The F4@B9 sample, which was prepared at 900 °C, exhibited an excellent performance (98.01 %) to activate peroxydisulfate (PDS) for the degradation of 2,4-dichlorophenol. Electron paramagnetic resonanceand chemical quenching experiments revealed that reactive oxygen radicals (ROS) including sulfate radical (•SO4-), hydroxyl radical (•OH), superoxide radical (•O2-), and singlet oxygen (1O2) existed in the F4@B9/PDS system. Furthermore, the micro-electrolysis process facilitated the generation of •O2- (12.35 %) and 1O2 (6.49 %) compared with the pure PDS system. Density functional theory revealed that, for the F4@B9-activated PDS process, the graphene shell of F4@B9 served as catalytic active sites as well. According to the correlation analysis, the iron specie of CFe15.1 was more favorable for the generation of ROS than α-Fe. Also, π-π* shake up, pyridinic N, graphitic N, and defects participated in the PDS activation. This study provides a new method for the preparation of high-performance catalysts from naturally grown biomass with high iron contents.

New insights into engineering the core size and carbon shell thickness of Co@C core-shell catalysts for efficient and stable Fenton-like catalysis.

Herein, we engineered the cobalt core size and carbon shell thickness of Co@C by molten salt electrolysis (MSE) to investigate the enhanced essence of decreasing core size as well as the shell thickness dependence-mediated transition of catalytic mechanisms. We found that the reaction activation energy (RAE) of Co@C/peroxymonosulfate (PMS) systems was intimately dependent on the core sizes for sulfamethoxazole (SMX) degradation. The smaller core size of 26 nm provided a lower RAE of 13.39 kJ mol-1. In addition, increasing carbon shell thicknesses of Co@C altered the catalytic mechanisms from a radical pathway of SO4•- and •OH to to a non-radical pathway of 1O2 and electron-transfer process (ETP), which were verified by experimental results and density functional theory (DFT) calculations. Interestingly, increasing carbon shell thicknesses promoted the charge transfer between Co metal slab and carbon shell, increased the adsorption energy of PMS molecule on the Co@C slab, and decreased the length of OO, which favoured the occurrence of non-free radical processes.

In-situ photoreduction strategy for synthesis of silver nanoparticle-loaded PVDF ultrafiltration membrane with high antibacterial performance and stability.

Ultrafiltration (UF) technology using polyvinylidene fluoride (PVDF) membrane has been widely applied to water and wastewater treatment due to its low cost and simple operation process. However, PVDF-based UF membrane always encountered the issue of membrane biofouling that greatly impacted the filtration performance. In this study, we prepare a silver nanoparticle (AgNP)-loaded PVDF (Ag/PVDF) UF membrane by an in-situ photoreduction method to mitigate the membrane biofouling. Different from the previously reported method, AgNPs were synthesized in-situ by a UV photoreduction process, in which Ag+ ions were reduced to zero-valent Ag nanoparticles by the photo-induced reducing radicals. Antibacterial experiments showed that the inhibition efficiency of Ag/PVDF membrane to Escherichia coli reached up to ~ 99% after antibacterial treatment for 24 h. In comparison with the pristine PVDF membrane, Ag/PVDF membrane possessed a lower water contact angle (83.7° vs. 38.1°), and its pure water flux increased by 23.7%, and a high bovine serum albumin (BSA) rejection efficiency was maintained. In addition, the high stability of the Ag/PVDF composite membrane was confirmed by the extremely low releasing amount of Ag. This study provides a novel strategy for the preparation of metal nanoparticle-incorporated Ag/PVDF ultrafiltration composite membrane showing favorable antibacterial performance and stability.

Biphase Co@C core-shell catalysts for efficient Fenton-like catalysis.

Despite the vital roles of Co nanoparticles catalytic oxidation in the Fenton-like system for eliminating pollutants, contributions of Co phases are typically overlooked. Herein, a biphase Co@C core-shell catalyst was synthesized by the electrochemical co-reduction of CaCO3 and Co3O4 in molten carbonate. Unlike the traditional pyrolysis method that is performed over 700 °C, the electrolysis was deployed at 450 °C, at which biphase structures, i.e., face-centered cubic (FCC) and hexagonal close-packed (HCP) structures, can be obtained. The biphase Co@C shows excellent catalytic oxidation performance of diethyl phthalate (DEP) with a high turnover frequency value (TOF, 28.14 min-1) and low catalyst dosage (4 mg L-1). Furthermore, density functional theory (DFT) calculations confirm that the synergistic catalytic effect of biphase Co@C is the enhancement for the breaking of the peroxide O-O bond and the charge transfer from catalysts to PMS molecule for the activation. Moreover, the results of radicals quenching experiments and electron paramagnetic resonance (EPR) tests confirm that SO4•-, •OH, O2•-, and 1O2 co-degrade DEP. Remarkably, 100% removals of three model contaminants, including DEP, sulfamethoxazole (SMX) and 2,4-dichlorophen (2,4-DCP), were achieved, either in pure water or actual river water. This paper provides an electrochemical pathway to leverage the phase of catalysts and thereby mediate their catalytic capability for remediating refractory organic contaminants.

Thermal reduction-desorption of cadmium from contaminated soil by a biomass co-pyrolysis process.

Thermal desorption is one of the methods commonly used for the remediation of contaminated soil. However, its suitability for the treatment of widespread Cd-contaminated soil was seldom investigated, because the desorption of Cd was found to be difficult, even at a high heating temperature. In the present study, a biomass co-pyrolysis (BCP) method is proposed for the thermal treatment of Cd-contaminated soil. The results showed that, when the mixture of biomass and contaminated soil was pyrolyzed at ~550 oC, the gaseous pyrolytic products (such as CO and hydrocarbon gases) from the biomass could chemically reduce the Cd(II) into volatile Cd0, thereby allowing the evaporation of vaporized Cd0 from the soil within a short operating time. The BCP method can achieve a highly efficient removal of Cd from the soil samples spiked with a large amount of Cd(II). The remediated soil, containing the remaining biochars, showed a good regreening potential and a significant decrease in Cd bioavailability. It also showed a good performance for the remediation of field soils from four contaminated sites (>92% removal efficiencies), and one of the treated soils could even meet the Cd screening level of agricultural land of China.

Sustainable phosphorus recovery from wastewater and fertilizer production in microbial electrolysis cells using the biochar-based cathode.

Reducing the energy consumption and electrode cost for electrochemical recovery of phosphorus (P) from wastewater is crucial for the large-scale application. In this study, biochar electrodes were investigated as the low-cost cathode in a microbial electrolysis cell (MEC) and this P-enriched biochar electrode was directly retrieved as P fertilizer after wastewater treatment. The Fe2+ salt modified biochar significantly increased the electrochemical performance of MECs due to the improved electrical conductivity and cathodic activity. Compared to the pristine biochar cathode, the current density of the MEC increased from 16.8 ± 0.2 A/m3 to 20.7 ± 0.8 A/m3, and the P removal increased from 28.8% ± 1% to 62.4% ± 3.5%. The power consumption was 0.25 ± 0.01 kWh/kg P which was more than one order of magnitude lower than the previous report. It was also demonstrated that the P enriched biochar amended soil improved the Pakchoi cultivation.

Degradation of 2,4-DCP using persulfate and iron/E-carbon micro-electrolysis coupling system.

The greenhouse gas carbon dioxide (CO2) was converted to a novel CO2 conversion material (electrolytic carbon, EC) by molten salt electrochemical conversion, which served as the carbon source to prepare an iron-carbon composite (Fe-EC). The composite was used to activate persulfate (PS) and degrade 2,4-dichlorophenol (2,4-DCP) in an aqueous solution. The effects of several essential operating parameters such as PS dosage and pH on 2,4-DCP degradation were investigated. The removal efficiency of 2,4-DCP (20 mg L-1) was 97.8% in the presence of Fe-EC (50 mg L-1) and PS (1 mmol L-1). Moreover, the average % reaction stoichiometric efficiency (RSE) (calculated for all selected times 5-60 min) was maintained at 23.07%. Electron paramagnetic resonance (EPR), classical radical scavenging experiments, and density functional theory (DFT) calculations were integrated for a mechanistic study, which disclosed that the active species in the system were identified as SO4⦁-, •OH, and O2⦁-. Moreover, the iron-carbon micro-electrolysis/PS (ICE-PS) system had a high tolerance to a wide range of pH, which would provide theoretical guidance for the treatment of organic pollutants in practical industrial wastewater.

Perdisulfate-assisted advanced oxidation of 2,4-dichlorophenol by bio-inspired iron encapsulated biochar catalyst.

To improve advanced oxidation processes (AOPs), bio-inspired iron-encapsulated biochar (bio-inspired Fe⨀BC) catalysts with superior performance were prepared from iron-rich biomass of Iris sibirica L. using a pyrolysis method under anaerobic condition. The obtained compounds were used as catalysts to activate perdisulfate (PDS) and then degradate 2,4-dichlorophenol (2,4-DCP), and synthetic iron-laden biochar (synthetic Fe-BC) was used for comparison. The highest removal rate of 2,4-DCP was 98.35%, with 37.03% of this being distinguished as the contribution of micro-electrolysis, greater than the contribution of adsorption (32.81%) or advanced oxidation (28.51%). The high performance of micro-electrolysis could be attributable to the formation of Fe (Iron, syn) and austenite (CFe15.1) with strong electron carrier at 700 °C. During micro-electrolysis, Fe2+ and electrons were gradually released and then used as essential active components to enhance the AOPs. The slow-releasing Fe2+ (K = 0.0048) also inhibited the overconsumption of PDS (K = -0.00056). Furthermore, the electrons donated from Fe⨀BC-4 were able to activate PDS directly. The electrons were enriched by the porous structure of Fe⨀BC-4, and the formation of the COFe bond in the π-electron system could also accelerate the electron transfer to activate PDS. Similar reactive oxygen species (ROS) were identified during the micro-electrolysis and AOPs, leading to similar degradation pathways. The higher does concentration of O2- generated during micro-electrolysis than during the AOPs also led to a greater dechlorination effect.

Molten Electrolyte-Modulated Electrosynthesis of Multi-Anion Mo-Based Lamellar Nanohybrids Derived from Natural Minerals for Boosting Hydrogen Evolution.

The multi-anion molybdenum-based nanohybrids, N-doped ß-Mo2C/MoP/MoOx (denoted as MoCPO), serving as a highly efficient catalyst for hydrogen evolution reaction (HER), are fabricated via a simple and scalable electrosynthesis in molten NaCl-KCl, which integrates pyrolysis/electroreduction/compounding into a one-pot strategy using polyphosphazenes (PPAs) and earth-abundant molybdenite (mainly MoS2) as precursors. The deliberately selected PPA and molten electrolyte ensure the unique lamellar nanostructures and the blending of multiple anions of C, N, P, and O in the obtained catalyst, specifically, triggering the in situ formation of the structural oxygen vacancies (VO) in MoCPO. The nature of the hybrids can be regulated by adjusting the synthesis condition. The optimized hybrid displays a low overpotential of 99.2 mV at 10 mA cm-2 for HER in 0.5 M H2SO4 and stays active over a broad pH range. The theoretical calculations reveal that VO in the hybrids serves as favorable active sites, thus contributing to the superior HER activity. Moreover, MoCPO is also effective for overall water splitting as a bifunctional catalyst.

Diffusion-layer-free air cathode based on ionic conductive hydrogel for microbial fuel cells.

High hydraulic pressure in air-cathode microbial fuel cells (MFCs) can lead to severe cathodic water leakage and power reduction, thereby hindering the practical applications of MFCs. In this study, an alternative air cathode without a diffusion layer was developed using a cross-linked hydrogel, oxidized konjac glucomannan/2-hydroxypropytrimethyl ammonium chloride chitosan (OKH), for ion bridging. The cathode was placed horizontally to avoid hydraulic pressure on its surface. Ion transportation was sustained with a minimal OKH hydrogel loading of 10 mg/cm2. A maximum power density of 1.0 ± 0.04 W/m2 was achieved, which was only slightly lower than the 1.28 ± 0.02 W/m2 of common air cathodes. Moreover, the cost of the OKH hydrogel is only $0.12/m2, which can reduce ~85% of the cathode cost without using the advanced polyvinylidene fluoride diffusion layer. Therefore, the development of this new diffusion-layer-free air cathode using conductive ionic hydrogel provides a low-cost strategy for stable MFC operation, thereby demonstrating great potential for practical applications of MFC technology.

Dissolved Silicate Enhances the Oxidation of Chlorophenols by Permanganate: Important Role of Silicate-Stabilized MnO2 Colloids.

Dissolved silicate is an important background constituent of natural waters, but there is little clarity regarding the effect of silicate on the oxidizing capability of permanganate (Mn(VII)) and on its efficiency for remediation applications. In the present study, we found that dissolved silicate, metasilicate or disilicate (DS), could significantly promote the oxidation of 2,4-dichlorophenol (2,4-DCP) by Mn(VII), and the extent of the promoting effect was even more evident than that of pyrophosphate (PP). The experiments showed that, unlike PP, DS was not capable of coordinating with Mn(III) ions, and the promoting effect of DS was not due to the oxidizing capability of complexed Mn(III). Instead, DS ions, as a weak base, could combine with the hydroxyl groups of MnO2 via hydrogen bonding to limit the growth of colloidal MnO2 particles. The DS-stabilized colloidal MnO2 particles, with hydrodynamic diameters less than 100 nm, could act as catalysts to enhance the oxidation of 2,4-DCP by Mn(VII). The best promoting effect of DS on the performance of Mn(VII) oxidant was achieved at the initial solution pH of 7, and the coexisting bicarbonate ions further improved the oxidation of 2,4-DCP in the Mn(VII)/DS system. Sand column experiments showed that the combined use of Mn(VII) and DS additive could mitigate the problem of permeability reduction of sand associated with the retention of MnO2 particles. This study not only deepens our understanding on the role of dissolved silicate in a Mn(VII) oxidation process but also provides an effective and green method to enhance the oxidizing capacity of Mn(VII)-based treatment systems.

Performance assessment of coupled green-grey-blue systems for Sponge City construction.

In recent years, Sponge City has gained significant interests as a way of urban water management. The kernel of Sponge City is to develop a coupled green-grey-blue system which consists of green infrastructure at the source, grey infrastructure (i.e. drainage system) at the midway and receiving water bodies as the blue part at the terminal. However, the current approaches for assessing the performance of Sponge City construction are confined to green-grey systems and do not adequately reflect the effectiveness in runoff reduction and the impacts on receiving water bodies. This paper proposes an integrated assessment framework of coupled green-grey-blue systems on compliance of water quantity and quality control targets in Sponge City construction. Rainfall runoff and river system models are coupled to provide quantitative simulation evaluations of a number of indicators of land-based and river quality. A multi-criteria decision-making method, i.e., Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) is adopted to rank design alternatives and identify the optimal alternative for Sponge City construction. The effectiveness of this framework is demonstrated in a typical plain river network area of Suzhou, China. The results demonstrate that the performance of Sponge City strategies increases with large scale deployment under smaller rainfall events. In addition, though surface runoff has a dilution effect on the river water quality, the control of surface pollutants can play a significant role in the river water quality improvement. This framework can be applied to Sponge City projects to achieve the enhancement of urban water management.

Spatiotemporal distribution and interaction of denitrifying functional genes in a novel DAS-NUA biofilter used for groundwater nitrate treatment.

A newly combined dewatered alum sludge (DAS) and neutralized used acid (NUA) biofilter has been constructed and investigated recently, aiming for improving nitrate (NO3--N) removal in simulated groundwater and exploring the spatiotemporal distribution of nirS and nosZ. The biofilter achieved 81.54% and 13.6 g N/ (m3 d) removal efficiency of NO3--N during the stabilization period. Spatiotemporal distributions of diversity and composition of nirS and nosZ varied approximately in two media with depths and time. Both DAS and NUA played important roles in attenuating nitrate because of predominant denitrifying genera functions, and the core differences were Rhodanobacter and Rhodobacter in DAS while Halomonas, Pseudogulbenkiania, and Cupriavidus in NUA. Acting as the strongly correlated genera, Magnetospirillum and Halomonas had a significantly positive or negative correlation with other dominant genera. Positive correlations existed among COD, TN, NO3--N, NO2--N, and both nirS and nosZ in the DAS filter, whereas the correlations were negative in the NUA filter. Particularly, the effluent concentration of NO3--N had a significantly negative correlation with the relative abundance of Rubrivivax and Pseudomonas. These results could be useful in adjusting the denitrification of nitrogen contaminants at the genetic level, especially in mitigating the influence of discharge of NO3--N on the process of groundwater restoration.

Bionic Preparation of CeO2-Encapsulated Nitrogen Self-Doped Biochars for Highly Efficient Oxygen Reduction.

This study reports the superior performance of novel carbonaceous materials, CeO2-encapsulated nitrogen-doped biochars [BC-Ce-X (X = 1 and 2)], for oxygen reduction reaction (ORR). The biomass precursor of this value-added biochar material was biomimetically prepared via a hydroponic operation in the Ce-enriched solution. The characterization results showed that CeO2 with large amounts of oxygen vacancies was stably embedded in the N self-doped biochars during the pyrolytic processes. The measured specific surface areas of cerium-free biochar (BC sample), BC-Ce-1, and BC-Ce-2 were 79, 566, and 518 m2/g, respectively. The BC-Ce-X (X = 1 and 2) showed excellent ORR performances with onset potentials of ∼0.90-0.91 V, which outperformed the commercial 10 wt % Pt/C and BC. Compared with Pt/C, the BC-Ce-2 had better methanol tolerance and stability. Also, BC-Ce-2 displayed excellent electrochemical activity for Zn/air batteries. Controlled experiments and density functional theoretical calculations illustrated the synergistic effect between the pyri-N/C centers and CeO2 with oxygen vacancies in ORR. The Lewis base sites, created by pyri-N and oxygen vacancies, greatly facilitated the chemisorption of O2 molecules.

Concentration-Dependent Enhancing Effect of Dissolved Silicate on the Oxidative Degradation of Sulfamethazine by Zero-Valent Iron under Aerobic Conditions.

Dissolved silicate, as a ubiquitous inorganic component in natural waters, is reported to depress the reactivity of zero-valent iron (ZVI) for reductive reactions under anoxic conditions, but it is unclear if the same inhibitory effect occurs for a ZVI/O2 system. In this study, the role of dissolved silicate for the reactivity of micron-sized ZVI (mZVI) was revisited under aerobic conditions, and different observations were found. Silicate had a volcano-type enhancing effect on the performance of the ZVI/O2 system for sulfamethazine (SMT) degradation. The results showed that, under a circum-neutral or alkaline pH condition (pH 6.0-9.0), the presence of dissolved silicate could significantly enhance the degradation of SMT because silicate coordinated with ferrous ions and further led to the generation of reactive oxygen species (ROS). This study suggests that silicate can act as both a ligand and corrosion inhibitor in a ZVI/O2 system: the coordination of silicate and ferrous iron accelerated the oxidative degradation of organic pollutants in an oxic aqueous solution, while the corrosion inhibitory effect of surface-bound silicate at higher concentrations may decrease the reactivity of the ZVI/O2 system, thereby offsetting the enhancing effect from the silicate-coordinated ferrous iron. This study not only redefines the role of naturally occurring silicate for a ZVI reaction system but also gives clues to develop high-efficiency ZVI/O2 technologies for water remediation.

Electric Field-Driven Interfacial Alloying for in Situ Fabrication of Nano-Mo2C on Carbon Fabric as Cathode toward Efficient Hydrogen Generation.

A binderless composite cathode for efficient electrocatalytic hydrogen evolution reaction (HER), Mo2C-decorated carbon cloth (denoted as CC/MC), is simply fabricated via a novel and unique strategy which involves a solid-solid phase interfacial electrochemical reaction between carbon fiber and bulk-MoS2 in molten NaCl-KCl (700 °C). MoS2, evenly coated on carbon cloth (CC), is electrochemically reduced in situ and readily reacts with the carbon fibers of CC current collector to form a Mo2C nanoparticle layer. The experiment and calculation results show that the applied electric field results in a declining migration barrier of Mo vacancies in Mo2C lattice, which promotes the diffusion of Mo atoms into carbon across the interfacial Mo2C layer, thereby impelling the combination of Mo with C in depth. The electrochemical tests indicate that the optimized cathode (CC/MC-2) exhibits a small overpotential of 134.4 mV at 10 mA cm-2 and stays stable for HER in acidic media. The catalytic capacity for N2 reduction of CC/MC-2 is analyzed. In addition, a Ni-doped Mo2C-modified carbon fabric electrode with enhanced HER activity (η10 = 96.6 mV) can be prepared through a similar process.

Understanding the electrode reaction process of dechlorination of 2,4-dichlorophenol over Ni/Fe nanoparticles: Effect of pH and 2,4-dichlorophenol concentration.

Herein, with the exploitation of iron and nickel electrodes, the 2,4-dichlorophenol (2,4-DCP) dechlorinating processes at the anode and cathode, respectively, were separately studied via various electrochemical techniques (e.g., Tafel polarization, linear polarization, electrochemical impedance spectroscopy). With this in mind, Ni/Fe nanoparticles were prepared by chemical solution deposition, and utilized to test the dechlorination activities of 2,4-DCP over a bimetallic system. For the iron anode, the results showed that higher 2,4-DCP concentration and solution acidity aggravated the corrosion within the electrode. The charge transfer resistance (Rct) values of the iron electrode were 703, 473, 444, and 437 Ω∙cm2 for the initial 2,4-DCP concentrations of 0, 20, 50, and 80 mg/L, respectively. When the bulk pH of the 2,4-DCP solution varied from 3.0, 5.0 to 7.0, the corresponding Rct values were 315, 376, and 444 Ω∙cm2, respectively. For the nickel cathode, the reduction current densities on the electrode at -0.75 V (vs. saturated calomel electrode) were 80, 106, and 111 µA/cm2, for initial 2,4-DCP concentrations of 40, 80, and 125 mg/L. The dechlorination experiments demonstrated that when the initial pH of the solution was 7.0, 5.0, and 3.0, the dechlorination percentage of 2,4-DCP by Ni/Fe nanoparticles was 62%, 69%, and 74%, respectively, which was in line with the electrochemical experiments. 10 wt.% Ni loading into Ni/Fe bimetal was affordable and gave a good dechlorination efficiency of 2,4-DCP, and fortunately the Ni/Fe nanoparticles remained comparatively stable in the dechlorination processes at pH 3.0.

H-bonding effect of oxyanions enhanced photocatalytic degradation of sulfonamides by g-C3N4 in aqueous solution.

In this study, the effect of oxyanions on the photodegradation of sulfonamides by graphitic carbon nitride (g-C3N4) was investigated. The results showed that the presence of disilicate (DS) could substantially improve the photodegradation of sulfamethazine (SMZ) in g-C3N4 aqueous suspension. The primary mechanism for the enhancing effect of DS was hydrogen bonding (H-bonding) interaction. The hydroxyl groups (OH) and bridging oxygen (SiOSi) of DS can form H-bonds with the amine groups of g-C3N4 particles and sulfonamides, therefore soluble DS can act as a bridge to enhance the transfer and adsorption of SMZ onto the surface of g-C3N4 particles. The presence of DS did not change the mechanism of photodegradation, but there was an optimal concentration for DS to achieve the strongest enhancing effect. H-bonding effect was also found for other oxyanions derived from weak acids, such as silicate, dihydrogen phosphate and borate ions, because the partial ionization of these oxyanions allowed the existence of hydroxyl groups to form H-bonds. The present study not only deepens our understanding of the interface process of the photodegradation of sulfonamides in g-C3N4 aqueous suspension, but also provides a potential method to enhance the photocatalytic degradation of antibiotics in wastewater streams.