First-order Reaction Rate Constants Research Articles

Application of environmentally friendly technologies for the management of nanofiltration concentrate from landfill leachate

In this study, the treatability of leachate nanofiltration (NF) concentrate using the modified Fenton process was investigated. The modified Fenton process employs an environmentally friendly oxidant (sodium percarbonate, SPC), an environmentally friendly catalyst (Fe2+), and environmentally friendly activators (electrooxidation-ultraviolet, EO-UV). The study aimed at enhancing the biological degradability of leachate NF concentrate and was conducted in two stages. In the first stage, the process variables of the SPC/Fe2+ process were optimized. In the second stage, combined processes were applied under optimum conditions. With the SPC/Fe2+ process under optimum conditions (pH: 5, SPC dose: 10 mM, Fe2+ concentration: 50 mM, reaction time: 60 min, pre-catalyst dosing), removal efficiencies of 53.5%, 47.1%, and 61.6% were obtained for chemical oxygen demand (COD), UV254, and color, respectively. After optimizing the operational parameters of the SPC/Fe2+ process, combined processes of EO/SPC/Fe2+ and UV/SPC/Fe2+ were applied, and higher pollutant removal efficiencies were achieved with the EO/SPC/Fe2+ process. Under optimum conditions, removal efficiencies of 75.3%, 80.5%, and 85.6% were achieved for COD, UV254, and color, respectively. The first-order reaction rate constant was 0.022 1/min for the EO/SPC/Fe2+ process. The biochemical oxygen demand (BOD)/COD, which increased from 0.040 to 0.080 with the SPC/Fe2+ process, reached 0.455 with the EO/SPC/Fe2+ process. Additionally, with the EO/SPC/Fe2+ process, the biologically degradable COD ratio of leachate NF concentrate increased from 16.7% to 83.5%, and the soluble COD fraction increased from 72.7% to 89.5%.

Preparation and photocatalytic performance of Sn-doped and BiOI-coupled dual modified Bi2WO6 composite

Sn doped and BiOI coupled dual modified Bi2WO6 photocatalytic material was prepared using hydrothermal route. The phase composition, morphology, surface area, elemental composition and oxidation state, as well as optical properties, were comprehensively characterized. Take the methylene blue (MB) as the model pollutant for photodegradation to estimate the photocatalytic property of the synthesized material. The prepared Bi2WO6- based composite material shows a flower-like structure assembled from nanosheets, with a surface area of 45.3 m2 /g and a bandgap width of 2.41 eV, enabling visible light responsiveness. The synergistic effect of Sn doping and BiOI coupling modification enhances the photocatalytic performance. The Sn-BiOI/Bi2WO6 photocatalytic composite material shows excellent photocatalytic activity, with complete degradation of MB after 40 minutes of illumination, and a first-order reaction rate constant (k) of 0.102 min–1 . Experimental evidence suggests that photoinduced holes are the main active species.

Prediction of atrazine degradation in soil based on XGBoost model.

We established the optimal model by using the automatic machine learning method to predict the degradation efficiency of herbicide atrazine in soil, which could be used to assess the residual risk of atrazine in soil. We collected 494 pairs of data from 49 published articles, and selected seven factors as input features, including soil pH, organic matter content, saturated hydraulic conductivity, soil moisture, initial concentration of atrazine, incubation time, and inoculation dose. Using the first-order reaction rate constant of atrazine in soil as the output feature, we established six models to predict the degradation efficiency of atrazine in soil, and conducted comprehensive analysis of model performance through linear regression and related evaluation indicators. The results showed that the XGBoost model had the best performance in predicting the first-order reaction rate constant (k). Based on the prediction model, the feature importance ranking of each factor was in an order of soil moisture > incubation time > pH > organic matter > initial concentration of atrazine > saturated hydraulic conductivity > inoculation dose. We used SHAP to explain the potential relationship between each feature and the degradation ability of atrazine in soil, as well as the relative contribution of each feature. Results of SHAP showed that time had a negative contribution and saturated hydraulic conductivity had a positive contribution. High values of soil moisture, initial concentration of atrazine, pH, inoculation dose and organic matter content were generally distributed on both sides of SHAP=0, indicating their complex contributions to the degradation of atrazine in soil. The XGBoost model method combined with the SHAP method had high accuracy in predicting the performance and interpretability of the k model. By using machine learning method to fully explore the value of historical experimental data and predict the degradation efficiency of atrazine using environmental parameters, it is of great significance to set the threshold for atrazine application, reduce the residual and diffusion risks of atrazine in soil, and ensure the safety of soil environment.

Kinetics and mechanistic investigation of the substitution from dinuclear Pt(II) complexes bridged by N,N’-bis(2-pyridylcarboxamide)phenylenediamines

The rates of substitution of the chloride ligand in dinuclear complexes, [Pt2(N,N'-bis(2-pyridylcarboxamide)-1,3-phenylenediamine)Cl4] (1), [Pt2(N,N'-bis(2-pyridylcarboxamide)-1,4-phenylenediamine)Cl4] (2), [Pt2(N,N'-bis(3-isoquinolylcarboxamide)-1,3-phenylenediamine)Cl4] (3) and [Pt2(N,N'-bis(3-isoquinolylcarboxamide)-1,4-phenylenediamine)Cl4] (4), by three bio-relevant nucleophiles, thiourea (TU), N,N-dimethylthiourea (DMTU) and N,N,N’,N’-tetramethylthiourea (TMTU), were investigated. The mononuclear analogue [Pt(N-phenylpyridine-2-carboxamide)Cl2] (5) was included to compare the results. The kinetics of the reactions were studied under pseudo first-order conditions in a methanol solution (I = 0.1 M LiCl) as a function of concentration and temperature using the stopped-flow spectrophotometer. The observed pseudo first-order rate constants for the substitution reactions of all the complexes were calculated from two well-separated steps and obey the rate law k obs (1 st /2 nd ) = k 2 (1 st /2 nd )[Nu]. The reactivity of the complexes decreases in the order 2 > 1 > 4 > 3 > 5. The conformational symmetry of the complexes as controlled by the phenylenediamine bridges, steric hindrance due to the bridges as well as the σ-donor capacity of the coordinated groups around the metal centers influence the reactivity of the dinuclear complexes. The low enthalpy (ΔH #) and negative intrinsic entropy (ΔS #) values support an associative mechanism of substitution. The kinetic data are supported by DFT calculations.

Insights into the electron transfer mechanisms of peroxydisulfate activation by modified metal-free acetylene black for degradation of sulfisoxazole

Herein, a modified metal-free acetylene black (MMF-AB) catalyst was synthesized by a simple solvothermal-calcination method and designed successfully to activate peroxodisulfate (PDS) for the degradation of sulfisoxazole (SIZ). Due to the doping of N, S and O metal-free elements, the modified catalyst showed excellent catalytic performance with 100% SIZ removal within 30 min. Pseudo first-order reaction rate constants (evaluating catalytic efficiencies and activity) of MMF-AB (kobs = 0.105 min−1) was 3 times higher than pure-AB (kobs = 0.029 min−1). Interestingly, it was demonstrated that the reaction system is based on the transfer of electrons from SIZ to PDS to realize an electron-transfer-based mechanism by the evidence of premixing, electron paramagnetic resonance (EPR) spectroscopy, salt-bridge experiments and electrochemical analyses. The introduction of recyclable filtration device solved the secondary pollution caused by the dispersion of the powdered catalyst in the treated water, which further proved the practicality and superiority of the MMF-AB catalyst.

A Fresh Perspective on the Impact of ZnTiO3 Coupling on the Microstructure and Photocatalytic Properties of TiO2 Fabricated at Varied Temperatures.

ZnTiO3/TiO2 composite photocatalysts were synthesized via the sol-gel technique, and the impact of varying heat treatment temperatures (470, 570, 670 °C) on their crystalline arrangement, surface morphology, elemental composition, chemical state, specific surface area, optical characteristics, and photocatalytic efficacy was systematically investigated. The outcomes revealed that, as the temperature ascends, pure TiO2 undergoes a transition from anatase to rutile, ultimately forming a hybrid crystal structure at 670 °C. The incorporation of ZnTiO3 engenders a reduction in the TiO2 grain dimensions and retards the anatase-to-rutile phase transition. Consequently, the specimens manifest a composite constitution of anatase and ZnTiO3. In contrast, for pure TiO2, the specimen subjected to 670 °C annealing demonstrates superior photocatalytic performance due to its amalgamated crystal arrangement. The degradation efficacy of methylene blue (MB) aqueous solution attains 91% within a 60-min interval, with a calculated first-order reaction rate constant of 0.039 min-1. Interestingly, the ZnTiO3/TiO2 composite photocatalysts exhibit diminished photocatalytic activity in comparison to pristine TiO2 across all three temperature variations. Elucidation of the photocatalytic mechanism underscores that ZnTiO3 coupling augments the generation of photogenerated charge carriers. Nonetheless, concurrently, it undermines the crystalline integrity of the composite, yielding an excess of amorphous constituents that impede the mobility of photoinduced carriers. This dual effect also fosters escalated recombination of photogenerated charges, culminating in diminished quantum efficiency and reduced photocatalytic performance.

Hydroxyl radical-driven transformations of bisphenol A and 2,4-dinitroanisole: Experimental and computational analysis.

This study used experimental and computational analysis to investigate the advanced oxidation of bisphenol A (BPA) and 2,4-dinitroanisole (DNAN). The pseudo first-order reaction rate constants depended on the molar peroxide ratio and were between 0.13 and 0.28 min-1 for BPA and between 0.018 and 0.032 min-1 for DNAN. The kinetic differences appear to be due in part to the energy requirements for oxidation, which depended on the reaction mechanism but were typically lower for BPA than they were for DNAN. Density functional theory (DFT) was used to develop transformation pathways that included experimentally-detected byproducts. The most energetically favored pathway for BPA oxidation begins with the formation of hydroxylated derivatives, while for DNAN, the most energetically favorable degradation pathway begins with the substitution of the methoxy group. Overall, these findings demonstrate the power of combining experimental and computational tools to reveal transformation mechanisms during water treatment. PRACTITIONER POINTS: Advanced oxidation transformations for two emerging water pollutants, bisphenol A and dinitroanisole, was investigated. The observed reaction kinetics depended on molar peroxide ratio in a manner that is in keeping with previous findings. Density functional theory-based analysis revealed reaction energy requirements and degradation pathways.

Effects of SnO2 coupling on the structure and photocatalytic performance of TiO2/sepiolite composites

The use of titanium dioxide in the degradation of water pollutants encounters several challenges, including particle agglomeration leading to a reduction in its specific surface area and a high rate of photogenerated electron-hole recombination, resulting in a lower quantum efficiency. Therefore, in this work, we first employed sepiolite to load titanium dioxide, mitigating particle agglomeration. Building upon this, tin dioxide was coupled with it to enhance the photogenerated charge separation. The SnO2/TiO2/sepiolite photocatalytic composites were synthesized using the sol–gel method at 450 ℃. The resulting composites underwent thorough characterization encompassing phase composition, morphology, chemical valence states, specific surface area, optical properties, and photocatalytic activity. The outcomes demonstrate an augmentation in the specific surface area of TiO2/Sep composites following the sepiolite (Sep) loading. Among these, the TiO2/Sep composite (with a Sep: TiO2 mass ratio of 10 %) exhibited the most favorable photocatalytic performance, displaying a first-order reaction rate constant of 0.010 min−1, surpassing that of pure TiO2 by a factor of 2.0. The introduction of SnO2 expedited the migration of photogenerated charge across interfaces, curbing the recombination of photogenerated pairs, thus enhancing quantum efficiency. In light of the presence of sepiolite, the addition of SnO2 further amplified the photocatalytic performance. Optimal results were achieved when the molar ratio of SnO2:TiO2 was set at 1:4, leading to the highest photocatalytic efficiency observed in the SnO2/TiO2/Sep composite. This composite exhibited a first-order reaction rate constant of 0.027 min−1, marking a notable 2.7-fold increase compared to the TiO2/Sep counterpart. The investigation of band potentials, charge transfer pathways, and the photocatalytic mechanism within SnO2/TiO2/Sep composite materials was conducted through a comprehensive analysis involving electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) valence band spectroscopy, electron paramagnetic resonance spectra (EPR) and active radical experiments.

Kinetics of ester-105 degradation by La/TiO2 photocatalysis

Lanthanum-doped titanium (La/TiO2) nano-photocatalysts were prepared using the sol-gel method and characterized by X-ray diffraction (XRD), zeta potential, and low-temperature nitrogen adsorption analyses. Ester-105, a flotation collector from beneficiation wastewater, was chosen as the target pollutant. The influence of the initial ester-105 concentration, pH, and photocatalyst dosage on the photocatalytic degradation of ester-105 was investigated. To examine the kinetics of the adsorption and photocatalytic degradation of ester-105, a Langmuir adsorption model and Langmuir-Hinshelwood kinetic models were established and discussed. The synthesized photocatalyst comprised anatase-phase TiO2, with an isoelectric point of pH = 6.5, specific surface area of 56.1626 m2·g−1, and average pore size of 7.78 nm. The maximum adsorption and the adsorption equilibrium constant of La/TiO2 for ester-105 were determined as 0.338 mg·g−1 and 1.008 L·mg−1, respectively. The first-order kinetic reaction rate constant (k) exhibited a linear relationship with the initial ester-105 concentration. The optimal pH for ester degradation was theoretically determined to be 6.95, and the optimum photocatalyst dosage was found to be 0.2739 g·L−1. Experiments confirmed that the photocatalytic degradation of ester-105 using La/TiO2 followed the Langmuir-Hinshelwood kinetics model, thereby providing a theoretical foundation for the photocatalytic degradation of ester-105 for industrial application.

Role of nitrogen dual reaction sites in N-doped graphene aerogels for synergistic sulfamethoxazole adsorption and peroxymonosulfate activation in Fenton-like process

Persulfate-based advanced oxidation technology is widely used in water treatment, and the key is to develop catalysts showing excellent performance. In this study, an N-doped graphene aerogel (N-GA-2) with a three-dimensional macroscopic structure was prepared by chemically reducing graphene oxide using ethylenediamine (EDA) and was used to activate peroxymonosulfate (PMS) for sulfamethoxazole (SMX) degradation. N-GA-2 has high pyridinic N content (5.84 at.%), and shows excellent catalytic performance in the activation of PMS. The SMX degradation rate was 94.11% within 90 min, and the first-order reaction rate constant was 0.0231 min−1. Furthermore, the adsorption of SMX on N-GA-2 was chemisorption, and the maximum adsorption capacity (qm) was 250.00 mg/g. Quenching experiments and electrochemical tests confirmed that the electron-transfer pathway was the main reason for SMX degradation. X-ray photoelectron spectroscopy and density functional theory revealed that pyridinic N, adjacent C atoms and electron-rich C = O functional groups were involved in the degradation of SMX. Specially, pyridinic N functioned as dual reaction sites for both SMX adsorption and PMS activation. The formation of SMX/N-GA-2* and N-GA-2/PMS* complexes, dominated by pyridinic N, enabled the completion of electron-transfer pathways. In addition, N-GA-2/PMS/SMX system demonstrated superior continuous catalytic performance in fluidized-bed experimental facility simulating practical applications, which can stably and sustainedly degrade SMX. This study focuses on the mechanism of electron transfer pathway induced by nitrogen dual reaction site in N-doped graphene aerogel and explores its potential application in engineering. This will provide basic theoretical support for the practical application of N-GA-2/PMS catalytic system.

Facile fabrication of BiOI/Bi2WO6 Z-scheme heterojunction composites with a three-dimensional structure for efficient degradation of pollutants

Three-dimensional BiOI/Bi2WO6 Z-scheme photocatalysts were synthesized by one-step hydrothermal method. Detailed characterization via SEM and TEM revealed that these photocatalysts exhibit a unique three-dimensional flower-like structure, composed of two-dimensional sheets. The results of photocatalysis mechanism analysis demonstrated that the BiOI/Bi2WO6 heterojunctions have formed a Z-scheme charge transfer mechanism. Specifically, electrons transfer from the Bi2WO6 conduction band to the BiOI valence band, facilitating both enhanced separation of photogenerated charges and the preservation of the strong reducibility of BiOI conduction band electrons and the strong oxidation of Bi2WO6 valence band holes. This dual effect leads to increased generation of free radicals and a consequent improvement in photocatalytic property. Remarkably, when the molar ratio of BiOI/Bi2WO6 is set at 40%, the first-order reaction rate constant reaches 0.089 min−1, which is nearly 5.9 times that of pure Bi2WO6.

One-step synthesis of highly active cotton floc like ZnO–BiOI: Visible-light photocatalytic performance, recovery and degradation mechanism

As a new technology for wastewater treatment and new energy development, semiconductor photocatalysis technology has been widely studied in recent year. In this study, a series of ZnO–BiOI (1:1, 1:2, 1:3, 1:3, 2:1, 2:3, 3:1, 3:2) binary composite photocatalysts were synthesized by one-step solvothermal method. XRD, SEM, TEM, HR-TEM, UV–vis DRS and PL characterization methods were used to analyze the physicochemical properties. Compared with pure ZnO, the band gap of ZnO–BiOI composite was narrower, the light absorption ability was enhanced, and the photogenerated electron-hole recombination probability was reduced. Among all the samples, ZnO–BiOI (3:2) had the best activity to degrade RhB, and the degradation rate reached 98% after 240 min under visible light, and the first-order reaction rate constant was 34.8 times that of pure BiOI. In addition, ZnO–BiOI (3:2) showed good stability in the cycle experiment. The interfacial electric field was formed in the photocatalytic process of ZnO–BiOI (3:2), which promoted more photogenerated electron-holes to participate in the oxidation reaction. The degradation process of organic matter was mainly through the oxidation of ·O2− and h+.

Enhanced plasmonic photocatalytic performance of C doped TiN nanocrystals through ultrathin carbon layers

Carbon-doped TiN nanoparticles on an ultrathin carbon layer, were successfully used for photocatalytic dye degradation synthesised by a simple calcination process. The resulting catalyst exhibited remarkable plasmonic photocatalytic performance under visible light irradiation. In comparison with benchmark rutile TiO2 and g-C3N4/TiO2 heterostructure catalysts, the first-order reaction rate constant of the developed catalyst improved approximately 34.2 and 6.5 times, respectively. The doping concentration of carbon and the crystal size of TiN nanoparticles, predominantly influenced by the amount of urea and calcination temperature, were identified as crucial factors governing the plasmonic photocatalytic activity. Density functional theory (DFT) calculations indicated that the introduction of carbon-sp bands into the TiN band structure promoted interband excitation of electrons and facilitated the generation of hotter holes, thereby enhancing the degradation of dyes and ultimately contributing to the superior photocatalytic activity observed.

Enhanced photocatalytic activity of p (BaSnO3)-n (anatase/rutile/brookite TiO2) heterojunction composites by efficient interfacial charge transfer

In the present work, new BaSnO3/TiO2 p-n heterojunction composite photocatalysts based on p-type BaSnO3 and n-type TiO2 with anatase/rutile/brookite three-phase coexisting were constructed. The microstructure and photocatalytic performance of the prepared composites were investigated. The results show that pure TiO2 (PT) consists of three phases including anatase, rutile and brookite. Mott-Schottky curves prove that BaSnO3 and TiO2 are coupled to form p-n heterojunctions, and the built-in electric field generated at heterogeneous interfaces promotes the separation of photogenerated charges and enhances the photocatalytic performance. When the Ba/Ti molar ratio is 5%, 5%BaSnO3/TiO2 (5%BT) exhibits the highest photocatalytic activity. The first-order reaction rate constant of 5%BT is 0.157 min–1, which is 1.8 and 2.2 times higher than that of commercial P25 (0.089 min–1) and PT (0.071 min–1), respectively. Furthermore, a mechanism of p-n heterojunctions improving the photocatalytic performance is proposed based on band potentials analysis and ESR results.

A visible light responsive Bi2S3/MIL-53(Fe) heterojunction with enhanced photocatalytic activity for degradation of tetracycline

Metal-organic frameworks (MOFs), as a new type of crystal materials, are considered a kind of promising photocatalysts. In this work, a novel Bi2S3/MIL-53(Fe) heterojunction photocatalyst was successfully prepared via a facile two-step method (hydrothermal and water bath). The characterization means, including XRD, SEM-EDS, FT-IR, XPS, PL, and UV–Vis, were employed to analyze the structural and morphological properties of Bi2S3/MIL-53(Fe). The photocatalytic performance of Bi2S3, MIL-53(Fe), and Bi2S3/MIL-53(Fe) was evaluated by the removal efficiency of the photocatalytic degradation of tetracycline (TC, 10 mg/L) under visible light irradiation (λ > 420 nm). The results show that the photocatalyst BSM-10 (the mass ratio of Bi2S3 to MIL-53(Fe) is 10:90) exhibits improved photocatalytic performance compared to Bi2S3 and MIL-53(Fe), showing the optimum photocatalytic activity (the degradation efficiency of TC is 90.9% within 120 min), and the corresponding first-order reaction rate constant is about 3 and 2 times higher than that of MIL-53(Fe) and Bi2S3, respectively. The improvement in photocatalytic activity is attributable to the efficacious separation of photogenerated electron-hole pairs and significant acceleration of charge transfer rate. Based on the free radical trapping experiment and ESR test results, combined with the band structure of MIL-53 (Fe) and Bi2S3, we speculate that a heterojunction is formed between MIL-53 (Fe) and Bi2S3, and the proposed Z scheme mechanism can well explain the enhanced catalytic activity of BSM-10. The Bi2S3/MIL-53 (Fe) heterojunction photocatalyst synthesized in this work has potential application value for removing the typical pollutant tetracycline from water.

Norfloxacin removal by ultraviolet-activated sodium percarbonate and sodium hypochlorite: process optimization and anion effect.

The efficiency of UV-activated sodium percarbonate (SPC) and sodium hypochlorite (SHC) in Norfloxacin (Norf) removal from an aqueous solution was assessed. Control experiments were conducted and the synergistic effect of the UV-SHC and UV-SPC processes were 0.61 and 2.89, respectively. According to the first-order reaction rate constants, the process rates were ranked as UV-SPC > SPC > UV and UV-SHC > SHC > UV. Central composite design was applied to determine the optimum operating conditions for maximum Norf removal. Under optimum conditions (UV-SPC: 1 mg/L initial Norf, 4 mM SPC, pH 3, 50 min; UV-SHC: 1 mg/L initial Norf, 1 mM SHC, pH 7, 8 min), the removal yields for the UV-SPC and UV-SHC were 71.8 and 72.1%, respectively. HCO3-, Cl-, NO3-, and SO42- negatively affected both processes. UV-SPC and UV-SHC processes were effective for Norf removal from aqueous solution. Similar removal efficiencies were obtained with both processes; however, this removal efficiency was achieved in a much shorter time and more economically with the UV-SHC process.

Effect of Ag Modification on the Structure and Photocatalytic Performance of TiO2/Muscovite Composites

Ag/TiO2/muscovite (ATM) composites were prepared by the sol-gel method and the effects of Ag modification on the structure and photocatalytic performance were investigated. The photocatalysts were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller surface area (BET), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectra (FTIR), photoluminescence spectra (PL) and ultraviolet-visible diffuse reflectance spectra (DRS). The photocatalytic activity of the obtained composites was evaluated by taking 100 mL (10 mg/L) of Rhodamine B (RhB) aqueous solution as the target pollutant. The muscovite (Mus) loading releases the agglomeration of TiO2 particles and the specific surface area increases from 17.6 m2/g (pure TiO2) to 39.5 m2/g (TiO2/Mus). The first-order reaction rate constant increases from 0.0009 min-1 (pure TiO2) to 0.0074 min-1 (150%TiO2/Mus). Ag element exists in elemental silver. The specific surface area of 1-ATM further increases to 66.5 m2/g. Ag modification promotes the separation of photogenerated electrons and holes and increases the visible light absorption. 1%Ag-TiO2/Mus (1-ATM) exhibits the highest photocatalytic activity. After 100 min, the rhodamine B (RhB) degradation degrees of PT, 150%TiO2/Mus and 1-ATM are 10.4%, 48.6% and 90.6%, respectively. The first-order reaction rate constant of 1-ATM reaches 0.0225 min-1, which is 25 times higher than that of pure TiO2.

Investigating the Extracellular-Electron-Transfer Mechanisms and Kinetics of Shewanella decolorationis NTOU1 Reducing Graphene Oxide via Lactate Metabolism

Microbial graphene oxide reduction is a developing method that serves to reduce both production costs and environmental impact in the synthesis of graphene. This study demonstrates microbial graphene oxide reduction using Shewanella decolorationis NTOU1 under neutral and mild conditions (pH = 7, 35 °C, and 1 atm). Graphene oxide (GO) prepared via the modified Hummers' method is used as the sole solid electron acceptor, and the characteristics of reduced GO (rGO) are investigated. According to electron microscopic images, the surface structure of GO was clearly changed from smooth to wrinkled after reduction, and whole cells were observed to be wrapped by GO/rGO films. Distinctive appendages on the cells, similar to nanowires or flagella, were also observed. With regard to chemical-bonding changes, after a 24-h reaction of 1 mg mL-1, GO was reduced to rGO, the C/O increased from 1.4 to 3.0, and the oxygen-containing functional groups of rGO were significantly reduced. During the GO reduction process, the number of S. decolorationis NTOU1 cells decreased from 1.65 × 108 to 1.03 × 106 CFU mL-1, indicating the bactericide effects of GO/rGO. In experiments adding consistent concentrations of initial bacteria and lactate, it was shown that with the increase of GO additions (0.5-5.0 mg mL-1), the first-order reaction rate constants (k) of lactate metabolism and acetate production increased accordingly; in experiments adding consistent concentrations of initial bacteria and GO but different lactate levels (1 to 10 mM), the k values of lactate metabolism did not change significantly. The test results of adding different electron transfer mediators showed that riboflavin and potassium ferricyanide were able to boost GO reduction, whereas 2,6-dimethoxy-1,4-benzoquinone and 2,6-dimethyl benzoquinone completely eliminated bacterial activity.

Generation of adsorbed atomic hydrogen by Pd(II) doped Fe(OH)2 enables ultra-fast reductive dechlorination of trichloroethylene

Trichloroethylene (TCE) is a notorious persistent pollutant in groundwater, while most reductive dechlorination processes result in the formation of toxic less-chlorinated by-products. In this work, adsorbed atomic hydrogen (H*) was produced by Pd(II) doped Fe(OH)2, which was used for ultra-fast reductive dechlorination of TCE without the formation of less-chlorinated by-products. When the Fe(OH)2 dosage is 0.5 mM and the Pd(II) dosage is 20 μM, TCE (42 μM) is completely removed in 60 min with the pseudo first-order reaction rate constant of 7.74 h−1. Radical quenching experiment and electrochemical analysis both confirmed that adsorbed H* rather than absorbed H* contribute to the reduction of TCE. Density function theory calculation demonstrated that small Pd clusters were more beneficial to TCE dechlorination than large Pd clusters. The pseudo first-order rate constant for TCE reduction in real groundwater was as high as 0.018 min–1, demonstrating the potential application of Pd/Fe(OH)2 in groundwater remediation.

Enhanced Photocatalytic Activity of Anatase/Rutile Heterojunctions by Lanthanum and Tin Co-Doping.

Anatase/rutile heterojunctions were prepared using the sol–gel method and modified by La/Sn single doping and co-doping. Sn doping promoted the transformation from anatase to rutile, while La doping inhibited the phase transformation. La and Sn co-doping showed an inhibitory effect. The co-doping of La and Sn did not increase visible-light absorption, but exhibited a synergistic effect on inhibiting the recombination of photogenerated electrons and holes, which improved the photocatalytic activity on the basis of single-element modification. The first-order reaction rate constant of La/Sn co-doped sample was 0.027 min−1, which is 1.8 times higher than that of pure TiO2 (0.015 min−1). Meanwhile, the mechanism of photodegradation of methylene blue (MB) by La/Sn co-doped anatase/rutile heterojunctions was discussed through electrochemical measurements and free-radical trapping experiments.