Order Kinetic Rate Constant Research Articles

Visible light photocatalytic response of Fe doped TiO2: Inactivation of Escherichia coli

Heterogeneous photocatalysis has been widely investigated for the removal of pollutants and pathogenic microorganisms. Various modified photocatalysts were developed for the beneficial use of solar light. E. coli inactivation by Fe doping of TiO2 (P-25) and sol–gel prepared (SynTiO2) was achieved upon solar irradiation in both isotonic (IsoT) and water matrix (WM) conditions. First order kinetic rate constants were comparatively higher for bare SynTiO2 both in IsoT (k = 0.254 min−1) and WM (k = 0.180 min−1) solutions. WM exerted an overall retardation effect for all photocatalysts except for 0.50 % Fe-TiO2 and 0.25 % Fe-SynTiO2. Release of intracellular components was followed by spectroscopic parameters as well as dissolved organic carbon (DOC) contents. E. coli cell destruction was related to the released protein, carbohydrate, and K+ ion contents. Solar photocatalytic inactivation of E. coli using novel sol–gel prepared TiO2 and Fe doped sol–gel TiO2 was successfully demonstrated as an alternative and promising method for disinfection purposes.

Dissolved oxygen enhanced piezo-photocatalytic performance in Ag dots-modified BaTiO3 nanoparticles for efficient degradation of multiple organic pollutants

Piezoelectric nanomaterials have attracted much attention due to their ability to modulate photo-excited carrier separation and migration under strain. Perovskite-structured BaTiO3 (BT) is a promising piezo-photocatalytic material due to its high piezoelectric coefficient and special phase structure. In this work, a series of x wt.% Ag/BT composites prepared by a two-step approach were developed for piezo-photocatalysis applications. The 0.8 wt.% Ag/BT showed an excellent piezo-photocatalytic performance for degrading 75.8 % Rhodamine B (RhB) in 60 min. Especially, the catalytic performances were strongly correlated with the atmosphere conditions of the catalyst. The piezo-photodegradation rate of RhB by 0.8 wt.% Ag/BT under O2 atmosphere reached 95.7 % in 40 min, and the first order kinetic rate constant (k) reached 0.06759 min−1, which was 9.9 and 2.4 times that of N2 and air condition, respectively. The Density functional theory (DFT) calculations further revealed that dissolved oxygen could enhance the material's adsorption of RhB. Compared with hydroxyl free radicals (OH) and holes (h+), superoxide radicals (O2–) play an indispensable role in the catalytic process through the trapping experiments and ESR analyses. Furthermore, the RhB degradation pathway and potential ecotoxicity were also proposed. This work is hoped to provide an understanding the mechanism of piezo-photocatalysis and bring new ideas for the development of piezo-photocatalysis catalysis for multifunctional environmental applications.

Analyzing the role of Ni dopant to change the structural, optical and photocatalytic properties of SnO2 nanoparticles

SnO2 and 5 wt% Ni doped SnO2 nanoparticles (SnO2:Ni NPs) were successfully synthesised by a template-free hydrothermal method. X-ray diffraction (XRD) patterns depicted polycrystalline nature of the NPs in rutile-type cassiterite phase with dominant (110) and (101) Bragg diffraction peaks. Rietveld refinement of XRD patterns supported single phase tetragonal crystal structure having space group P42/m n m. With Ni doping, crystallite size of NPs decreased from 39 nm to 35 nm whereas lattice strain increased from 3.56 × 10−3 to 3.99 × 10−3. This is attributed to the substitution of Sn4+ ion by Ni2+ ions. The morphology of the SnO2 NPs also changed from regular spherical shape to elongated irregular shape upon Ni doping. The dominant Raman peak obtained at 634 cm−1 matched with the signature peak for rutile SnO2 (Raman A1g mode). Further, we observed disappearance of E g mode due to Ni doping, which indicated the formation of oxygen vacancies. Also, XPS analysis indicated an increase of oxygen vacancy concentration in the doped NPs due to charge imbalance between Sn4+ and Ni2+. The direct optical band gap of SnO2 increased from 3.97 eV to 4.11 eV when doped with 5 wt% Ni and it is ascribed to Burstein–Moss effect. Irrespective of higher optical band gap of SnO2:Ni NPs, they showed enhanced photocatalytic activity to degrade Rhodamine B (RhB) dye molecules under UV-visible irradiation. The first order kinetic reaction rate constants for degradation of RhB were found to be 0.014 min−1 and 0.045 min−1 in case of SnO2 and SnO2:Ni NPs respectively. The enhanced photocatalytic activity in SnO2:Ni NPs is explained by relating to the formation of more oxygen vacancies and chemisorptions of O2 and H2O molecules followed by generation of radicals. This work demonstrates the superiority of SnO2:Ni NPs for use as photocatalytic material for industrial waste water treatment.

Enhanced visible light sensitized photoreaction by mixed phase titania nanotubes

In this work, we demonstrate the synthesis of mixed crystalline TiO2 nanotubes (TiNT) using a rapid breakdown anodization process and investigate its application in visible light photocatalytic degradation of rhodamine-B (RhB) dye pollutant. Nanotubes with different anatase to rutile crystalline phases were achieved during thermal annealing by tuning the amount of perchlorate ions. Increasing the rutile content decreased the nanotubes' bandgap and surface area. Photocatalytic studies of TiNT with different crystalline phase ratios revealed promising RhB degradation under visible light compared to commercial TiO2. Herein we propose the humidity conditioning (99% relative humidity) of TiNT as a surface modification method to enhance the –OH group on the oxygen defective sites. FTIR and XPS analysis of the TiNT before and after surface modification showed significant change in the surface –OH groups. The surface area normalized apparent-first order kinetic rate constant was higher for all the TiNTs than commercial TiO2. We report for the first time the higher photocatalytic activity of the humidity conditioned nanotubes with high –OH groups compared to the respective catalyst with less –OH group. The simple method proposed for –OH group incorporation shows a possible way of developing an efficient photocatalyst without complex surface modification techniques.

Enhanced electro-activity of nickel phosphide by pre-treatment for efficient hydrogen sulfide elimination

Electrochemical sulfide oxidation is a promising approach for sulfide removal from wastewater or biogas due to low energy and chemical consumption. In this work, nickel phosphide was facilely electrodeposited on stainless steel (SS/Ni-P) and comprehensively evaluated as anode catalyst for sulfide oxidation. Electrochemical property analysis suggested that SS/Ni-P had low polarization resistance (109.10 Ω) and high electrochemical active surface area (Cdl = 1.3 mF/cm2). The sulfide removal efficiency of SS/Ni-P achieved 95.00 ± 3.55 % at 1.42 V vs RHE within 48 h, which was 2.60 times and 3.62 times of that by SS/Ni and SS anodes, respectively. The first order kinetic rate constant of SS/Ni-P for sulfide removal was 0.0315 ± 0.0061 h-1, superior than that of the reported single nickel atom based catalyst with stainless steel substrate. Pre-treating SS/Ni-P under a constant external potential for 10 s further improved the electroactivity on sulfide oxidation due to the enhancement of the electrochemical active surface area by 46.56%. Further analysis of the chemical state changes during the sulfide oxidation process revealed that the Ni from Ni-P was the real active center, which formed Ni-S precursors to promote polysulfide formation. This work provided a highly efficient sulfide oxidation anode material for sulfide containing wastewater and biogas treatment.

Solar-light-driven LaFe x Ni1- x O3 perovskite oxides for photocatalytic Fenton-like reaction to degrade organic pollutants.

LaFexNi1−xO3 perovskite oxides were prepared by the sol–gel method under various conditions, including different pH values (pH 0 and pH 7) and different calcination temperatures (500–800 °C) as well as different Fe/Ni ratios (1/9, 3/7, 5/5, 7/3, 9/1). The samples were examined by XRD, DRS, BET, and SEM to reveal their crystallinity, light-absorption ability, specific surface area, and surface features, respectively. The photocatalytic Fenton reaction was conducted using various LaFexNi1−xO3 perovskite oxides to decompose the methylene blue molecules. Accordingly, the synthesis condition of pH 0, calcination temperature at 700 °C, and Fe/Ni ratio = 7/3 could form LaFe0.7Ni0.3O3 perovskite oxides as highly efficient photocatalysts. Moreover, various conditions during the photocatalytic degradation were verified, such as pH value, catalyst dosage, and the additional amount of H2O2. LaFe0.7Ni0.3O3 perovskite oxides could operate efficiently under pH 3.5, catalyst dosage of 50 mg/150 mL, and H2O2 concentration of 133 ppm to decompose the MB dye in the 1st order kinetic rate constant of 0.0506 s−1.

Ozone Kinetic Studies Assessment for the PPCPs Abatement: Mixtures Relevance

The increasing consumption of pharmaceutical and personal care products (PPCPs) by humankind has been causing an accumulation of contaminants (commonly referred to as contaminants of emerging concern), in effluents and water resources. Ozonation can be used to improve the removal of these contaminants during water treatment to alleviate this burden. In this work, the degradation of methyl (MP), propylparaben (PP), paracetamol (PCT), sulfamethoxazole (SMX), and carbamazepine (CBZ) by ozonation was assessed both for individual compounds and for mixtures with increasing complexity (two to five compounds). Ozonation was performed at pH3 to gain an insight on the exclusive action of molecular ozone as oxidizing agent. The degradation of contaminants was described as a function of time and transferred ozone dose, and the corresponding pseudo-first order kinetic rate constants (k’) were determined. PPCPs were degraded individually within 1.5 to 10 min. CBZ was the most quickly degraded (k’ = 1.25 min−1) and MP the most resistant to ozone (k’ = 0.25 min−1). When in the mixture, the degradation rate of the contaminants was slower. For parabens, the increase of the number of compounds in the mixture led to an exponential decrease of the k’ values. Moreover, the presence of more PPCPs within the mixture increased energy consumption associated with the treatment, thereby reflecting higher economic costs.

Photocatalytic degradation of acetaminophen in water via ultraviolet light and titanium dioxide thin films part II: chemical and kinetic aspects

Abstract Among the large family of emergent pharmaceutical contaminants, we find acetaminophen (ACE) that critically needs to be removed from wastewater. Advanced Oxidation Process (AOP) have proven effective in the degradation of large molecular contaminants from water. To the best of our knowledge this is the first study reported on the degradation of ACE based on immobilized TiO2 thin films. In an effort to increase the understanding of the efficiency of the degradation process, an in-depth investigation of the effects of the structure, i.e., coating layers and the amount of surface, i.e., number of coated slides used, is needed. Transparent, anatase-form TiO2 thin films were prepared via the sol-gel method (Rawal, S., S. Buer, J. R. Sanders, and P. E. Arce. 2021. “Photocatalytic Degradation of Acetaminophen from Water Solutions Via Thin Films. Part I: Synthesis and Characterization of TiO2 Thin Films.” International Journal of Reactor Engineering [Accepted]) and deposited onto glass microscope slides using a novel spraying technique, with coatings ranging from one to 10 layers. This contribution summarizes the effect of several key factors including initial concentration of the ACE, the number of coating layers (6, 8, and 10) on the glass slides and the number (4 and 6) of slides on the degradation levels for three selected media, e.g., acid, neutral and base. Comparisons studies, supported by statistical analysis between two different sets (4 and 6) of slides with discussion of potential physical-chemical reasons behind the behaviors are reported. Finally, global, first order kinetic rate constants are also reported for the different conditions used in the investigation. Although further research would be needed, in general the results are promising for the potential degradation of ACE in continuous flow systems by using immobilized TiO2 on surfaces as thin films.

Adsorption of Triclosan onto Organically Modified-Magadiite and Bentonite

The removal of triclosan, a widely used antibacterial agent in personal care products, from water was investigated by using dioctadecyldimethylammonium modified magadiite (2C18-MAG) and bentonite (2C18-BT) as the adsorbents. The adsorption kinetics were discussed, and the kinetic data were described by pseudo-second order model. The pseudo-second order kinetic rate constant of the triclosan adsorption on 2C18-MAG was 2.5 times larger than that on 2C18-BT. Langmuir and Freundlich adsorption models were employed to describe the results to discuss the interactions between triclosan and the adsorbents. The adsorption process was governed by the intermolecular interactions between triclosan and the intercalated surfactant of the adsorbents. The highest adsorbed amounts were 534 mg/g and 422 mg/g for 2C18-MAG and 2C18-BT, respectively. The efficient adsorption of triclosan on 2C18-MAG indicates the great opportunity of organically modified layered silicates as the adsorbent for the removal of organic contaminants in aqueous environment.

Grafting of reactive dyes onto lignocellulosic material: Application for Pb(II) adsorption and electrochemical detection in aqueous solution

Triplochyton scleroxylon (Ayous) sawdust was modified by grafting two reactive dyes (Reactive Red 120 (RR120) and Reactive Black 5 (RB5)) inspired by the strategy used for cellulosic fibers dyeing. The visual appearance as well as the infrared spectra and the point of zero charge determination confirm the effective attachment of the dyes onto sawdust. The anionic charges resulting from the grafted dyes were exploited for Pb(II) biosorption and electrochemical detection in aqueous solution. The presence of dyes grafted onto Ayous sawdust (SA) greatly improves its affinity for Pb(II) biosorption as confirmed by the increase of the pseudo-second order kinetic rate constant, especially in the case of RR120 modified sawdust (SA-RR120). Moreover, the maximum adsorption capacities obtained from the Langmuir model (207 µmol g−1, 281 µmol g−1 and 298 µmol g−1 respectively for SA, SA-RB5 and SA-RR120) confirmed the improvement in adsorption resulting from sawdust dyeing. Used as glassy carbon electrode (GC) modifiers, the functionalized sawdust improved the electrochemical detection of Pb(II). After optimization of the experimental parameters, sub-nanomolar detection limits were obtained (1.3 nM, 0.7 nM and 0.4 nM for GC/SA, GC/SA-RB5 and GC/SA-RR120 respectively). In addition to such improvements in Pb(II) biosorption and trace-level detection, these materials also showed appreciable selectivity and excellent performance in real media samples.

Electro-enhanced adsorptive removal of ciprofloxacin from aqueous solution on graphite felt

In this study, enhanced electrosorption removal of ciprofloxacin is investigated using graphite felt electrodes. The effect of operating parameters like pH, applied voltage, electrolyte concentration, and initial concentration on the removal of ciprofloxacin and enhancement in adsorption capacity of graphite felt was studied. The adsorption isotherm and kinetics were studied. Cyclic voltammogram showed no significant redox peaks at the operated experimental conditions. The adsorption capacity was increased from 0.617 mg g−1 at open circuit voltage to 1.915 mg g−1 at 1.0 V and the corresponding pseudo first order kinetic rate constants were increased from 0.069 min−1 to 0.111 min−1. The adsorption capacity and kinetics observed to be high at pH 3.0 and 10.0 compared to pH 7.0. The electrosorption process performance increased with increasing applied voltage (OCV to 1.5 V) and reduced at high electrolyte concentration (0.1–1.0 M Na2SO4). Experimental data was fitted to Langmuir and Freundlich adsorption isotherm models. The electrosorption results proposed that the adsorption rate and adsorptive capacity can be significantly enhanced by electrochemical polarization with the greater affinity derived between the charged ciprofloxacin species and graphite felt. Mechanism of electrosorption removal of ciprofloxacin at different pH is proposed based on the experimental observations.

OH radicals reactivity towards phenol-related pollutants in water: temperature dependence of the rate constants and novel insights into the [OH-phenol]˙ adduct formation.

Substituted phenols are known to readily react with the hydroxyl radical (OH˙), which is the most powerful atmospheric oxidant and is also most often used in advanced oxidation processes (AOP) for wastewater treatment. We report temperature-dependent (278.15-318.15 K) second order kinetic rate constants for the aqueous-phase reactions of OH˙ with phenol and four substituted phenols: catechol, phloroglucinol, pyrogallol and 3-methylcatechol, with the last two measured for the first time. The constructed Hammett plots for mono- and di-substituted phenols have the potential to be further applied for predicting the reaction rate constants of other substituted phenols at 298.15 K. This will significantly facilitate the optimization of AOP and improve the predictive capabilities of atmospheric multiphase models in the future. Moreover, an advancement in the understanding of the underlying mechanism, i.e. OH˙ addition to the aromatic ring is made by theoretical calculations at the M06-2X level. We demonstrate that the position of substituents on the aromatic ring is important for the [OH-phenol]˙ adduct formation, which is supported by the experiment and theoretical calculations. Adjacent and nonadjacent electron donor/acceptor substituents differently impact the interplay between the activation energy and entropy. We also show that explicit solvation has to be accounted for in theoretical models in order to explicitly describe the formation of the transition state.

Facile preparation of novel Sb2S3 nanoparticles/rod-like α-Ag2WO4 heterojunction photocatalysts: Continuous modulation of band structure towards the efficient removal of organic contaminants

In order to fabricate the recyclable catalyst with enhanced photocatalytic degradation and stability, rod-like α-Ag2WO4 (n-type) modified Sb2S3 (p-type) chalcogenide were prepared by wet-impregnation method. The physico-chemical properties were characterized by X-ray diffraction, micro-Raman spectroscopy, UV–vis diffuse reflectance spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and Brunauer–Emmett–Teller analysis. UV–vis spectra show the Sb2S3 chalcogenide extends the visible light absorption of the synthesized composites when compared to that of pristine α-Ag2WO4. The photocatalytic degradation of prepared samples was investigated by MB, RhB and MO under the visible light irradiation. The highest photocatalytic degradation efficiency (91.23% of MB dye within 60 min) is observed for 25 wt% Sb2S3/α-Ag2WO4 nanocomposite when compared to other photocatalysts. The pseudo-first order kinetic rate constant of 25 wt% Sb2S3/α-Ag2WO4 (4.20 × 10−2 min−1) photocatalyst is 3.7 and 5.7 times higher than Sb2S3 and α-Ag2WO4 respectively. The colorless toxic pollutant tetracycline hydrochloride used as a model pollutant and it under go degradation of 53.06% after 180 min and reaction rate constant is about 4.1 × 10−3 min−1 over 25 wt% Sb2S3/α-Ag2WO4 photocatalyst. The radical trapping measurement reveals that h+ and O2– radicals the key reactive species in the suspension of Sb2S3/α-Ag2WO4 photocatalyst, which decompose the MB dye efficiently. Moreover, a possible photocatalytic mechanism is proposed based on the trapping results with enhanced photocatalytic activity for the efficient separation of photogenerated e−-h+ pairs, the excellent oxidation and reduction capabilities of the Sb2S3/α-Ag2WO4 heterojunction catalysts. The recycling experiments result reveals that Sb2S3/α-Ag2WO4 (25 wt%) nano-composite maintained good stability and an active photocatalyst after the five-cycle tests. The present study provides the novel insight into the fabrication of α-Ag2WO4 based photocatalysts that improved the visible light photodegradation efficiency of organic contaminants in the industrial wastewater.

Role of impregnated nano-photocatalyst (SnxTi(1-x)O2) inside mesoporous silica (SBA-15) for degradation of organic pollutant (Rhodamine B) under UV light

SBA-15 of high specific surface area (507 m2/g) and pore volume (1.05 cm3/g) [due to the presence of hexagonally arranged 8.26 nm pore diameter], was synthesized by sol-gel method and impregnated with different mole ratios of Sn to Ti, in order to prepare TiO2-SBA-15, Sn0.05Ti0.95O2-SBA-15, Sn0.08Ti0.92O2-SBA-15 and SnO2-SBA-15 photocatalysts. The average SBA-15 particle diameter was 740 nm. Impregnation of photocatalyst inside the SBA-15 pores were confirmed by electron microscopy and pore-size measurement. The anatase phase of TiO2-SBA-15 shifted to an anatase-rutile phase, after Sn-doping. A decrease of impregnated catalyst size (amongst the four catalysts), from 6.7 to 6.1 nm, due to lattice strain was confirmed by X-ray diffraction. From X-ray photoelectron spectroscopy, the oxidation states for TiO2-SBA-15 and SnO2-SBA-15 were found to be Ti4+ and Sn4+, respectively. It remained unchanged after Sn-doping of catalyst too. Subsequent UV-light based photocatalytic degradation of Rhodamine B, an organic pollutant, was conducted under various pH conditions. At pH 4.5, amongst these catalysts, Sn0.05Ti0.95O2-SBA-15 shows the highest activity (pseudo-first order kinetic rate constant of 1.36 h−1). The intermediate products during degradation were identified by HR-LC/MS and GC/MS. The temporal changes in Rhodamine B concentration both from UV-Vis absorbance and HR-LC/MS measurements were consistent too.

Kinetics of Reductive Degradation of 2,4-dinitroanisole (DNAN) Using Mg-Based Bimetals

Technology advancements and modern use of explosives have led to the development of insensitive munitions such as 2,4-dinitroanisole (DNAN). Treatment systems using zero-valent iron (ZVI) and Fe-based bimetals are well-known, however, Mg-based bimetals can be advantageous over iron because of the more negative reduction potential and relative insensitivity to pH conditions. This work reports on the use of ZVMg and Mg-bimetals (Mg/Cu, Mg/Ni, Mg/Zn) to treat pure compound aqueous solutions and wastewater containing DNAN. Kinetic experiments were carried out in bench-scale batch reactors at unadjusted initial pH, 0.5% solids-to-liquid ratio (S/L), and 10:1 Mg to catalytic metal ratio. The results, modelled with a pseudo-first order kinetic expression, are used to determine reaction rate constants via nonlinear regression. For pure DNAN aqueous solutions, the pseudo-first order kinetic rate constants are 0.119, 0.102, 0.020, and 0.009 min−1 for Mg/Cu, Mg/Zn, Mg/Ni, and ZVMg, respectively. Reaction rate constants for DNAN wastewater are 0.114, 0.046, and 0.021 min−1 for Mg/Cu, Mg/Zn and Mg/Ni, respectively. Parametric studies investigated the impact of catalytic metal, reagent dose, and initial pH on DNAN degradation. Reagent dose levels tested were 0.25, 0.50 and 0.75% S/L. Initial pH, lowered with acetic acid (pH range 3.3–4.0), significantly enhanced reaction rates of all bimetal pairs and ZVMg yielding half-lives between 0.7–1.4 min. The bimetal pair showing the fastest kinetics at unadjusted initial pH, Mg/Cu, was characterized in constant temperature experiments. Under identical conditions (unadjusted initial pH, 0.5% S/L, 10:1 Mg: Cu), the activation energy of DNAN degradation by Mg/Cu is 8.47 kJ/mol.

Mechanisms on the impacts of humic acids on persulfate/Fe2+-based groundwater remediation

Persulfate (PS) has been increasingly applied for in situ chemical oxidation of organic contaminants in groundwater, while the impacts of humic acids (HAs) on the efficiency of persulfate/Fe2+-based remediation are not well understood. This study examined the effects of HAs originating from different places, including three commercial HAs and two soil HAs, on 2,4-dinitrotoluene (DNT) degraded by PS/Fe2+. DNT degradation by PS/Fe2+ was dependent on the types and concentrations of HAs and pH in solution. The positive correlation between the first order kinetic rate constant of DNT degradation by PS/Fe2+/HAs and the conditional stability constant (KM) indicates that the complexation of HAs with Fe3+ was beneficial to the degradation of DNT. The first order kinetic rate constant of DNT degradation by PS/Fe2+/HAs correlated well with their absorbance intensity of HAs at 465 or 665 nm. High positive correlation coefficients indicated that π-electrons of HAs strongly influenced DNT degradation, which was consistent with the results provided by solid-state 13C NMR spectra. Two-dimensional correlation spectroscopy (2DCOS) analysis confirmed that the fulvic-like fraction of HAs is prior to the humic-like fraction complexed with Fe3+.

Enhanced photocatalytic ozonation of organic pollutants using an iron-based metal-organic framework

The photocatalytic activity of metal-organic frameworks (MOFs) is drawing great attention in the field of environmental remediation. However, the efficiency of MOFs still remains low because of the rapid recombination of valence band holes and conduction band electrons (a.k.a., charge carriers). The combination of photocatalysis and electron acceptors such as ozone are believed to be an efficient strategy to reduce the charge carrier recombination. Herein, we report that photocatalytic ozonation (PCO) using an Fe-based MOF (MIL-88A(Fe)) has greater destruction than photocatalysis and/or catalytic ozonation in terms of 4-nitrophenol (4-NP) degradation and mineralization. It is worth noting that our Fe-based MOF has a large number of Lewis acid sites (LAS). The pseudo-first order kinetic rate constants (k) of 4-NP degradation using PCO, photocatalysis and catalytic ozonation systems are 0.1632, 0.0143 and 0.0840 min−1, respectively. The TOC removal of 4-NP in the PCO system is approximately 75.4% ([4-NP] = 100 ppm, ozone input dosage = 1.5 mg/min-L, UV light intensity = 3.46 × 10-6 Einstiens/L-s, treatment time = 30 min) and this is much greater than those of photocatalysis (17.6%) and catalytic ozonation (38.7%). Most importantly, both the k value and TOC removal in the PCO system are much higher than the sum of those in other two processes, implying a strong synergistic effect in the PCO process. Mechanistic studies were conducted using electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) measurements and demonstrate that the synergistic effect may originate from the enhanced photoinduced carrier separation using ozone as an electron acceptor. Furthermore, OH, O2−, and 1O2 are found to be the principal reactive oxygen species (ROS) for 4-NP degradation and mineralization. Integrating the analysis of band structure, EPR and scavenging experiment results, ozone is not only able to reduce charge carrier recombination but also can be catalytically decomposed to generate more ROS on the LAS of MIL-88A(Fe). This study provides deep insights into the use of MOFs as effective advanced oxidation processes (AOPs).

Bioelectrochemical decolorization of a reactive diazo dye: Kinetics, optimization with a response surface methodology, and proposed degradation pathway

Bioelectrochemical systems (BESs) have shown great potential for azo dye removal. However, comprehensive evaluation of the bioelectrochemical decolorization performance for reactive diazo dyes remains limited, particularly the kinetics and operation parameter optimization. This study evaluated the decolorization of the diazo dye Reactive Black 5 (RB5) in BESs, particularly with regard to kinetics, parameter optimization using response surface methodology (RSM), and the degradation pathway. The results indicated that the pseudo–first–order kinetic rate constant of RB5 decolorization increased from 0.023 ± 0.001 to 0.146 ± 0.008 h−1 with a decrease in cathode potential from −400 mV to −500 mV. RSM optimization suggested that the linear effects of RB5 concentration, cathode potential and hydraulic retention time (HRT), interaction of RB5 concentration with cathodic HRT, and the quadratic effect of cathodic HRT were most influential on the bioelectrochemical decolorization of RB5. Further, the decolorized RB5 products in the BESs were characterized by ultraviolet–visible spectrophotometry, Fourier-transform infrared spectroscopy, and liquid chromatograph–mass spectrometry. From this, a potential decolorization mechanism is proposed based on cleavage of azo bonds.

Isotope fractionation in atrazine degradation reveals rate-limiting, energy-dependent transport across the cell membrane of gram-negative rhizobium sp. CX-Z

In the biological mass transfer of organic contaminants like atrazine, the cellular membrane limits bioavailability of pesticides. We aimed to illustrate the roles of cellular membrane physiology and substrate uptake (e.g., passive diffusion and energy-dependent transport) on the limitations of bioavailability in atrazine biodegradation by Gram-negative strain Rhizobium sp. CX-Z. Compound-specific stable isotope analysis revealed energy-dependent transport across cellular membrane led to bioavailability limitations in atrazine biotransformation. Carbon isotope fractionation (ε(C) = −1.8 ± 0.3‰) was observed and significantly smaller in atrazine biodegradation by Rhizobium sp. CX-Z than that expected in acid hydrolysis (ε(C) = −4.8 ± 0.4‰) and hydrolysis by the pure enzyme TrzN (ε(C) = −5.0 ± 0.2‰). However, isotope fractionation was restored in membrane-free cells of Rhizobium sp. CX-Z (ε(C) = −5.4 ± 0.2‰) where no cellular membrane limits substrate uptake. When respiratory chain was inhibited by rotenone, the pseudo-first order kinetic rate constants (0.08 ± 0.03 h−1, 0.09 ± 0.03 h−1) was observed to be statistically less than in the control group (0.23 ± 0.02 h−1, 0.33 ± 0.02 h−1), demonstrating that energy-dependent transport dominated atrazine transfer across the cellular membrane. Therefore, our results revealed energy-dependent transport across cellular membrane existing in Gram-negative strain Rhizobium sp. CX-Z determines bioavailability of atrazine in biotransformation process even at high concentration.

Synthesis of peroxidase‐encapsulated sodium cellulose sulphate/poly‐dimethyl‐diallyl‐ammonium chloride biopolymer via polyelectrolyte complexation for enhanced removal of phenol

AbstractPeroxidases have attracted significant interests in enzymatic wastewater treatment strategies. In this work, jicama peroxidase (JP) was extracted from jicama skin peels and used for the degradation of phenol under free and immobilized conditions. The crude enzyme extract demonstrated enzymatic activity of 1.6 ± 0.1 U mL−1. Sodium cellulose sulphate/poly‐dimethyl‐diallyl‐ammonium chloride (NaCS‐PDMDAAC) spherical capsules were synthesized and immobilized with crude JP to generate JP beaded capsules with an average diameter of 5.05 mm ± 0.16 mm. Phenol biodegradation analysis showed that the free and immobilized JP capsules demonstrated optimum working pH values of 7 and 6, respectively, and both systems maintained JP catalytic functionalities over a broad range of H2O2 concentration before H2O2 inhibition. The optimal temperature range for phenol removal was from 25°C to 40°C for both free and immobilized JP with lower removal efficiency above 45°C due to thermal denaturation. Due to diffusive mass transfer limitation, immobilized JP capsules required a longer reaction time of 15 hr for optimal phenol removal efficiency of >95%, whereas free JP achieved the same efficiency in 13 hr. The first order kinetic rate constants for free and immobilized JP capsules were determined to be 1.21 hr−1 and 1.02 hr−1, respectively. JP capsules maintained reusability up to 4 cycles at the highest removal efficiency of >95% with no regeneration.