Pseudo-first Order Kinetic Constants Research Articles

Performance and mechanic insights into potassium-oxygen co-doping graphic carbon nitride for UV photocatalytic oxidation of carbamazepine

Graphitic carbon nitride (g-C3N4) has good prospect in the field of photocatalysis, but its small specific surface area and low photogenerated carrier separation efficiency limit the large-scale application in photocatalytic wastewater treatment. In this study, the one-step thermal polymerization method was employed to synthesize potassium and oxygen co-doped g-C3N4 (OCN-3), which was used in photocatalytic degradation of carbamazepine (CBZ). Compared with the original g-C3N4, the pseudo first-order kinetic constant of CBZ degradation by OCN-3 was increased from 0.00820 min−1 to 0.17529 min−1 under UV irradiation. The results of competitive oxidation kinetics experiment demonstrated that ·OH played a main role in CBZ degradation. The photoelectric experiments and calculation based on density functional theory revealed that potassium and oxygen atoms can not only regulate the local electron density, but also reduce the band gap width and promote electron transfer as well as photogenerated carrier separation. Furthermore, OCN-3 was loaded on carbon cloth to prepare supported photocatalyst, which can be conveniently applied in continuous wastewater treatment reactor, and the results shows that the degradation efficiency of CBZ remains over 90% within 600 min continuous operation when the hydraulic retention time was 1.25 h.

Enhancing photocatalytic g-C3N4/PVDF membranes through new insights into the preparation methods

Fibrous membranes are crucial on the filtration of pollutants from air and water, but continued use can lead to a failure in effectiveness due to pollutant accumulation. To enhance durability, incorporating photocatalytic submicroparticles into these membranes appear as a solution.Here, we prepared a set of polyvinyl difluoride (PVDF) fibrous membranes modified with graphitic carbon nitride (g-C3N4) using three different methodologies. Their photocatalytic efficiency was investigated using phenol as model pollutant compound under visible light irradiation.Using g-C3N4 fibrous membranes modified by electrospinning blend a pseudo first-order kinetic constant (kapp) of 2.51 × 10-4 min-1 was observed for phenol degradation after 240 min reaction. Despite minimal particle adhesion the thermal treatment increased kapp to 5.41 × 10-4 min-1. The membranes prepared via chemical activation of PVDF exhibited the highest photocatalytic activity (kapp of 21.7 × 10-4 min-1). This superior activity was attributed to covalent bonds between PVDF and g-C3N4, allowing the formation of oxidative species.

Radiation-induced preparation of nanoscale CoO@graphene oxide for activating peroxymonosulfate to degrade emerging organic pollutants

In this study, ionizing radiation was used to induce the in-situ formation of highly dispersed nanosized cobalt oxide on the surface of graphene oxide (R-Co-GO), which was highly effective for activating PMS to degrade sulfamethoxazole (SMX). R-Co-GO had the highest catalytic activity when 150 μL cobalt chloride hexahydrate solution was used in the precursor, and the pseudo first-order kinetic constant of SMX degradation was 0.07 min−1 with high mineralization efficiency (63.1 %) and high PMS utilization efficiency. The sulfate radicals and high-valent cobalt oxo were mainly responsible for SMX degradation. Mechanism analysis showed that cobalt active site dominated in PMS activation, which was responsible for the formation of sulfate radicals and high-valent cobalt oxo; while the carbon framework contributed to the formation of singlet oxygen. The R-Co-GO-150 had good catalytic activity and stability in five cycling experiments, in which SMX was completely degraded and the concentration of dissolved Co was below 0.1 mg/L. In addition, the R-Co-GO-150/PMS system could also degrade phenol, bisphenol A, atrazine and nitrobenzene effectively, confirming its wide applicability. This study provided a facile method to uniformly disperse the metal oxides on the surface of carbon materials, and an effective system for the removal of emerging organic pollutants from the actual wastewater.

Sulfamethoxazole degradation by Ni2+ doped Fe2O3 on a nickel foam in peroxymonosulfate assisting photoelectrochemical oxidation system: Performance, mechanism and degradation pathway

In this work, to promote the catalytic efficiency of Fe2O3 and achieve the facile retrieve and recycle from the solution, Ni2+ doped Fe2O3 in-situ growing on a nickel foam (NF) (Ni-Fe2O3/NF) was fabricated using NF as the Ni2+ internal doping source and the substrate support and used in the peroxymonosulfate (PMS) assisting visible-light photoelectrochemical oxidation (EC + Photo + catalyst + PMS) system for sulfamethoxazole (SMX) degradation. Benefiting from more Fe2+ and oxygen vacancies generation after Ni2+, and the enhanced electrical conductivity owing to NF substrate, the optimum Ni-Fe2O3/NF(II) exhibited excellent catalytic efficiency. 100% of SMX was removed in 10 min in the EC + Photo + Ni-Fe2O3/NF(II) + PMS system and the pseudo-first order kinetic constant (kobs) was 45.10 × 10-2 min−1, being about 9.80 folds of powder Fe2O3. Meantime, due to the employed loading method benefits in the Ni-Fe2O3 uniformly and steady loading on NF, Ni-Fe2O3/NF(II) demonstrated the excellent stability and recycle ability. Reactive oxygen species (ROSs) quenching and electron paramagnetic resonance evidenced that photo-induced hole (h+), hydroxy radical (•OH) and superoxide radical (•O2−) contributed to SMX degradation. And the SMX degradation pathways were deduced according to the determined degraded products and density functional theory (DFT) calculation. This study developed one convenient separation and recovery catalyst suitable for EC + Photo + catalyst + PMS system for efficient and environmentally friendly antibiotics removal in water.

Electrochemical Treatment of Arsenic in Drinking Water: Effect of Initial As3+ Concentration, pH, and Conductivity on the Kinetics of Oxidation

Many technologies for the treatment of arsenic-containing drinking water are available, but most of them are more effective on arsenic oxidized forms. Therefore, the pre-oxidation of As3+ is necessary. The electrochemical processes represent a very promising method due to the simultaneous oxidation of compounds using electrochemical conditions and the reactive radicals produced. In this work, As3+ oxidation was experimentally studied at a pilot scale using an electrochemical oxidation cell (voltage: 10 V; current: 1.7 A). The effect of the initial arsenite concentration, pH, and conductivity of drinking water on the oxidation of As3+ into As5+ was investigated. The results showed that the initial As3+ concentration strongly directly influences the oxidation process. Increasing the initial arsenite concentration from 500 to 5000 µg L−1, the pseudo-first order kinetic constant (k) strongly decreased from 0.521 to 0.038 min−1, and after 10 min, only 21.3% of As3+ was oxidized (vs. 99.9% in the case of As3+ equal to 500 µg L−1). Slightly alkaline conditions (pH = 8) favored the electrochemical oxidation into As5+, while the process was partially inhibited in the presence of a more alkaline or acidic pH. The increase in conductivity up to 2000 µS cm−1 enhanced the kinetic of the oxidation, despite remaining on the same order of magnitude as in the case of conductivity equal to 700 µS cm−1. After 10 min, 99.9 and 95% of As3+ was oxidized, respectively. It is the opinion of the authors that the influence of other operational factors, such as voltage and current density, and the impact of the high concentration of other pollutants should be deeply studied in order to optimize the process, especially in the case of an application at full scale. However, these results provide helpful indications to future research having highlighted the influence of initial As3+ concentration, pH, and conductivity on the electrochemical oxidation of arsenic.

Simultaneous removal of triclosan and nitrate by a stable denitrifying microbial consortium

The co-existence of antibiotics and nitrate in common in the aquatic environment, so the simultaneous removal of antibiotics and nitrate is necessary, but still challenge. In this study, a stable denitrifying microbial consortium capable of degrading triclosan was isolated from a long-term operated denitrifying bioreactor used for biological nitrate removal. The microbial consortium consisted of Pseudomonas (93.47 %), Burkholderia (1.56 %) and Cupriavidus (1.17 %) based on high-throughout sequencing analysis. The denitrification efficiency was higher under anoxic condition than that under aerobic condition. However, the accumulation of nitrite was observed under anoxic condition, with maximal concentration of 10.2 mg/L. Triclosan had negative impact on denitrification under both aerobic and anoxic conditions. The pseudo first-order kinetic constant of denitrification was 0.0303 h−1 and 0.0468 h−1 under aerobic and anoxic conditions, respectively. Dechlorination of triclosan was observed under aerobic condition but not under anoxic condition. Hydroxylated-triclosan, 2,4-dichlorophenol and phenol were identified as intermediate products of triclosan degradation.

Electron transfer-based peroxydisulfate activation by waste herb residue biochar: Adsorption versus surface oxidation

Waste herb residue biochar (WBC) was synthesized to activate peroxydisulfate (PDS) for the removal of different micropollutants. WBC prepared at 700 °C (WBC700) exhibits discrepant adsorption and PDS catalytic performance to three pharmaceuticals and four phenolic compounds. At 60 min reaction time, the adsorptive removal by 0.5 g/L WBC700 varied from 31.3% (clofibric acid) to 97.6% (4-chlorophenol), while the apparent removal ranged from 36.1% (clofibric acid) to 99.5% (4-chlorophenol) when 0.5 g/L WBC700 and 1.0 mM PDS were applied. The oxidation of the micropollutants involves electron transfer mechanism via the surface-confined metastable reactive complexes (WBC-PDS*), which was verified by electrochemical tests, quenching experiments, electron paramagnetic resonance, Fourier transform infrared and in-situ Raman spectroscopy. The observed pseudo first-order kinetic constant (kobs) of organic removal did not exhibit a good correlation with its electrochemical redox descriptor (half-wave potential, φ1/2, for example) as reported in the previous studies. Instead, the surface oxidation rate constant (koxid), determined from a dynamic model considering liquid-solid mass transfer of micropollutant and the sequent surface oxidation by WBC-PDS* complexes, was highly related to φ1/2. In parallel, the liquid-solid mass transfer coefficient (KLa) of micropollutant was obtained from a similar model excluding the surface oxidation, and kobs showed a more significant association with KLa than with adsorption capacity (Qe). This study provides a promising approach to understand the role of adsorption and surface oxidation in an electron transfer-dominated persulfate activation process.

Supercritical Water Oxidation of Aniline, Nitrobenzene, and Indole: Effect of Catalysts on Nitrogen Conversion Mechanism

Certain undesired N-containing products like ammonia, nitrate, and organic-N species have become the roadblocks to supercritical water oxidation (SCWO) application. This study examined the mechanisms for total nitrogen (TN) removal by catalytic SCWO. By comparing pseudo-first order kinetic constants of TN removal, our findings showed that heteropolyacids took a significant part in TN removal for nitrobenzene, and Cu(NO3)2 achieved the best TN removal performance for aniline, nitrobenzene, and indole since both Cu(II) and NO3- could accelerate N2 formation via the reduction of nitrate and the oxidation of ammonia by NO2. and .OH. Distribution of N-containing species revealed that adding catalysts could generally facilitate the conversion of nitrogen gas from organic-N, while it cannot accelerate N2 production from ammonia and nitrate. According to the DFT result, conceivable degradation pathways of aniline, nitrobenzen, and indole were proposed involving denitrification, ring-open, and mineralization.

One-step solvothermal synthesis of wood flour carbon fiber/BiOBr composites for photocatalytic activation of peroxymonosulfate towards sulfadiazine degradation: Mechanisms comparison between photo, chemical and photo-chemical oxidation processes

Facile preparation of novel catalysts which can effectively activate peroxymonosulfate (PMS) under visible light is of great significance for rapid degradation of refractory organic chemicals in water. Herein, one-step solvothermal process was introduced to prepare carbon nanofiber incorporated bismuth oxybromide (BiOBr/SCF) composites, in which commercial wood flour was in-situ converted to carbon fiber with graphitic structure and incorporated with BiOBr via the process. At the existence of PMS, the prepared composites exhibited prominent visible-light photocatalytic degradation capability towards sulfadiazine (SDZ) with satisfying adaptability and recyclability. Specifically, the apparent pseudo-first order kinetic constant of BiOBr/SCF-180/PMS/visible light system (0.0724 min−1) exceeded those of both BiOBr/SCF-180/PMS (0.0462 min−1) and BiOBr/SCF-180/visible light (0.0111 min−1) systems. An integrated mechanism in the BiOBr/SCF/PMS/visible light system was elucidated through comparing the mechanisms amongst photo-oxidation, chemical oxidation and photo-chemical oxidation systems, in which photo-induced electron and hole, Bi3+/Bi5+ redox couple, graphitic structure and oxygen functional groups in the SCF all participated in the generation and conversion of the active species. The possible SDZ degradation pathway was also proposed. This work demonstrates a novel strategy to prepare high-efficient catalysts in the field of wastewater treatment.

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.

Destruction of valsartan using electrochemical and electrochemical/persulfate process. Kinetics, identification of degradation pathway and application in aqueous matrices

In this paper, the electrochemical oxidation (EO) of antihypertensive drug valsartan (VAL) on a boron-doped diamond anode was investigated. The impact of current density (1.25–25 mA/cm2), initial solution pH (3−10), valsartan concentration (0.25–1.5 mg/L), supporting electrolyte (0.1 M sulfate or chloride ion), and the water matrix (bottled water (BW), wastewater (WW), pure water (UPW) and UPW spiked with various water constituents) was systematically investigated. The apparent, pseudo-first order kinetic constant was found to increase with increasing current density and decreasing pH, VAL concentration and matrix complexity. Notably, the use of chloride as the supporting electrolyte was less efficient than the rather “inert” sulfate. The addition of persulfate (50–250 mg/L) in the EO process significantly enhanced performance, i.e. a 4-fold rate increase was recorded for the degradation of 0.5 mg/L VAL at 12.5 mA/cm2 in UPW added with 250 mg/L persulfate. VAL degradation is accompanied by the formation of various transformation products (TPs), seven of which were identified by UPLC-ESI-MS analysis. Major pathways include cyclization, hydroxylation, cleavage of the amide bond, and decarboxylation-dealkylation of the tertiary amine group reactions; the identified TPs were common regardless of the addition of persulfate, however, their distribution depended on the rate of VAL degradation.

Efficient activation of peroxymonosulfate by copper supported on polyurethane foam for contaminant degradation: Synergistic effect and mechanism

The occurrence of tetracycline (TTC) in the environment can exacerbate microbial selection pressure and trigger bacterial resistance, raising potential risks to the ecosystem and public health. Here, we report that copper supported polyurethane foam (Cu-NC) can efficiently activate PMS to degrade TTC. Results demonstrated that the degradation rate of TTC was 91.3% and the pseudo first-order kinetic constant of 0.0762 min−1 was achieved after 40 min reaction at pH 5.0. Activation of PMS by Cu-NC was proposed to proceed via two sequential processes, which was different from the conventional mechanism for sulfate radical generation. Cu0 initially reacts with dissolved oxygen to generate H2O2 and Cu(I)(s) in situ in the solid form. Then Cu(I)(s) solves the relative instability of low-valent transition metal ions in aqueous solution, thus improving the activation efficiency of PMS. A novel mechanism for Cu(I)(s) activation of PMS to generate HO• was proposed and elucidated through outer-sphere interaction (electrostatic bonding) and acid-base theory. Superoxide radical and Cu0 accelerate the Cu(II)/Cu(I) redox, overcoming the rate-limiting step in Fenton-like reaction. Cu-NC showed an excellent cycling stability (80.8% removal efficiency after fifth run) in PMS activation with low Cu ion leaching (＜0.2 mg/L). The Cu-NC/PMS system also exhibited satisfactory removal of TTC in the presence of various water matrices. This study can deepen the understanding of the generation of HO• in the PMS activation process and provide a promising strategy for pollutants degradation in wastewater treatment.

Enhanced redox activity and oxygen vacancies of perovskite triggered by copper incorporation for the improvement of electro-Fenton activity

ABO3 perovskite oxides doped with cation substitutions have been proved to change the inherent electronic and structural properties of perovskite. However, the role of perovskites substituted by B sites element in tailoring their electronic structure, crystal structure and surface chemical reaction on the degradation of organic pollutants by heterogeneous electro-Fenton (EF) process still remained obscure. Herein, the incorporation of Cu in LaCoO3 perovskite (LaCoxCu1−xO3−δ) was designed as heterogeneous EF catalyst for almost completely removal of target pollutant ciprofloxacin (CIP) within 120 min. The results showed that incorporation of Cu could effectively improve EF activity due to the enhancement of redox activity and oxygen vacancies (OVs) of LaCoxCu1−xO3−δ, which synergistically promoted the activation of hydrogen peroxide to hydroxyl radical (·OH). Furthermore, the superoxide free radical (O2−) was remarkably increased due to the electron-rich OVs and the redox pairs of Co2+/Co3+ and Cu+/Cu2+. Meanwhile, the pseudo-first order kinetic constant of the degradation process was investigated to evaluate the degradation effect of LaCoxCu1−xO3−δ. Finally, the degradation mechanism was investigated by EPR and scavenger experiments, which unraveled the important role of cation substitutions in perovskite oxides for the improvement of heterogeneous EF activity. The results provided insights into the incorporation strategy in perovskite oxides for improving heterogeneous EF activity in a rational approach.

An electroanalytical method for monitoring acid hydrolysis reactions using thick-film modified electrodes

Many organic compounds of pharmaceutical interest undergo unwanted reactions that reduce their effectivity or even generate harmful products. One of the many possible mechanisms for these degradation reactions is acid hydrolysis. We propose the use of the thick-film modified electrode setup to follow the acid hydrolysis reaction of water-soluble compounds that contain protonatable sites. We focus on the determination of the first order or pseudo-first order kinetic constant in the aqueous phase. The developed procedure is presented using a model for the transfer of protonated species at liquid|liquid interfaces coupled with an electron transfer process at the solid|liquid interface. Moreover, we experimentally validate this strategy by determining the kinetic constant for the degradation of tylosin A in acidic solutions.

Heterogeneous Catalytic Ozonation of Aniline-Contaminated Waters: A Three-Phase Modelling Approach Using TiO2/GAC

This work aims to study the sustainable catalytic ozonation of aniline promoted by granular active carbon (GAC) doped with TiO2. Aniline was selected as a model compound for the accelerator manufacturing industries used in the manufacture of rubber due to its environmental impact, low biodegradability, and harmful genotoxic effects on human health. Based on the evolution of total organic carbon (TOC), aniline concentration measured using high performance liquid chromatography (HPLC), pH and ozone concentration in liquid and gas phase, and catalyst loading, a three-phase reaction system has been modelled. The proposed three-phase model related the ozone transfer parameters and the pseudo-first order kinetic constants through three coefficients that involve the adsorption process, oxidation in the liquid, and the solid catalyst. The interpretation of the kinetic constants of the process allowed the predominance of the mechanism of Langmuir–Hinshelwood or modified Eley–Rideal to be elucidated. Seven intermediate aromatic reaction products, representative of the direct action of ozone and the radical pathway, were identified and quantified, as well as precursors of the appearance of turbidity, with which two possible routes of degradation of aniline being proposed.

Synergistic effect of Co(II) doping on FeS activating heterogeneous Fenton processes toward degradation of Rhodamine B

Iron-based heterogeneous Fenton systems have been widely proposed for recalcitrant contaminants degradation. However, low efficiency of H2O2 decomposition and Fe(II)/Fe(III) recycling quite limited their applications. In this work, Co-doped iron sulfide (FeS) was successfully prepared through a modified hydrothermal method, and characterized by XRD, FESEM, HRTEM, XPS and BET. With Co(II) substitution, FeS structure transformed from pyrrhotite to mackinawite. The 10% Co-FeS was highly effective in H2O2 activation toward Rhodamine B (RhB) degradation. The pseudo first-order kinetic constant of 10% Co-FeS was 0.323 min−1, which was 31.4 and 85 times higher than that of CoS2 and FeS, respectively. Quenching experiments and EPR analysis illustrated that •OH was the dominant radicals for RhB degradation and the role of Co(II) in H2O2 direct decomposition was negligible. Batch experiment suggested that the excellent catalytic performance of 10% Co-FeS were ascribed to: (i) Co incorporation into FeS structure facilitated electron transfer between S species and Fe3+, thus accelerating Fe(II)/Fe(III) conversion on the surface, and (ii) more active sites were exposed. The Co-doped FeS exhibited high stability with low Fe/Co leaching and great recyclability. This novel strategy brought potential insights to develop highly efficient catalyst like metal sulfides for wastewater treatment.

Cobalt doped iron oxychloride as efficient heterogeneous Fenton catalyst for degradation of paracetamol and phenacetin

Cobalt doped iron oxychloride (Co-FeOCl) was synthesized and employed as catalyst in Fenton degradation of paracetamol (APAP) and phenacetin (PNCT) for the first time. The catalytic performance was evaluated by means of various parameters including catalyst load, hydrogen peroxide (H2O2) dose and pH value. The high removal of APAP (87.5%) and PNCT (76.0%) was obtained under conditions of 0.2 g/L Co-FeOCl and 0.5 mM H2O2 at pH 7.0, with calculated pseudo-first order kinetic constants of 0.031 min−1 for APAP and 0.023 min−1 for PNCT. Particularly, quenching tests and in situ electron spin resonance (ESR) tests were employed for the identification of the reactive oxygen species (ROS) in system. Hydroxyl radical (·OH) and superoxide radical (O2−·) were the primary ROS in Co-FeOCl/H2O2 system. A possible mechanism for H2O2 activation by Co-FeOCl catalyst was proposed as well. Finally, the formation of typical disinfection by-products (DBPs) decreased slightly in Co-FeOCl/H2O2 pre-oxidation. However, stability and reusability of Co-FeOCl were deactivated in the consecutive three cycles.

Study of intermediate by-products and mechanism of the photocatalytic degradation of ciprofloxacin in water using graphitized carbon nitride nanosheets

The photocatalytic degradation of the antibiotic ciprofloxacin in water was carried out with nanosheets of graphitic carbon nitride (g-C3N4) as catalyst and visible light irradiation using low-power (4 × 10 W) white light LEDs. The aim of this study was to identify the intermediate by-products formed during the degradation and to propose a pathway for CIP degradation. To achieve this goal, photocatalytically degraded CIP solutions were analysed by liquid chromatography coupled to high-resolution mass spectrometry using a QTOF instrument. The accurate mass and the MS/MS data of the detected ions allowed us to determine the elementary composition of eight by-products and to propose the chemical structures for seven of them. Three of these by-products have been reported for the first time and the elementary composition of a fourth one that had been wrongly reported in the literature was accurately established. CIP degradation followed a pseudo-first order kinetics with a pseudo-first order kinetic constant of 0.035 min−1. In addition, a study of the influence of several scavengers showed that only the presence of triethanolamine dramatically reduced the pseudo-first order kinetic constant (0.00072 min−1), pointing out that the reactive species were the holes produced in the catalyst. Finally, the main pathway of CIP degradation seems to be the attack to the piperazine group by ·OH radicals, following heterocycle breakup and the subsequent loss of two of its carbon atoms as CO2 molecules, and then defluorination, oxidation and cleavage of the cycles of this intermediate.

Three-dimensional photoelectrocatalytic degradation of the opaque dye acid fuchsin by Pr and Co co-doped TiO2 particle electrodes

Herein, Pr and Co co-doped TiO2 onto flake graphite as particle electrodes were prepared and utilized for the opaque dye acid fuchsin degradation in a three-dimensional photoelectrocatalytic system. Scanning electron microscopy, Brunauer-Emmett-Teller, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy demonstrated that Pr and Co were successfully co-doped onto the TiO2 particles and largely enhanced their surface properties and photocatalytic activity. The co-doped Pr–Co/TiO2 flake graphite particle electrodes denominated reliable acid fuchsin degradation performance under various influencing factors with the optimized operational conditions as electrolyte concentration of 0.02 mol/L, external bias voltage of 6 V, electrodes dosage of 6.67 g/L, initial pH of 2, and initial AF concentration of 20 mg/L, and aeration-free. This gave a pseudo-first order kinetic constant of 0.1313 min−1. Over 90% of AF was removed within 40 min owing to the primary contribution of hydroxyl radicals. Multiple intermediates via photoelectrocatalytic degradation of acid fuchsin were identified and a possible removal pathway was thus proposed. The three-dimensional particle electrodes photoelectrocatalytic reactor hold great potential for opaque dye wastewater treatment.

Kinetics study of CO2 absorption in potassium carbonate solution promoted by diethylenetriamine

In this work, characterization and kinetics of CO2 absorption in potassium carbonate (K2CO3) solution promoted by diethylenetriamine (DETA) were investigated. Kinetics measurements were performed using a stirred cell reactor in the temperature range of 303.15–323.15 K and total concentration up to 2.5 kmol m−3. The density, viscosity, physical solubility, CO2 diffusivity and absorption rate of CO2 in the solution were determined. The reaction kinetics between CO2 and K2CO3 + DETA solution were examined. Pseudo-first order kinetic constants were also predicted by zwitterion mechanism. It was revealed that the addition of small amounts of DETA to K2CO3 results in a significant enhancement in CO2 absorption rate. The reaction order and activation energy were found to be 1.6 and 35.6 kJ mol−1, respectively. In terms of reaction rate constant, DETA showed a better performance compared to the other promoters such as MEA, EAE, proline, arginine, taurine, histidine and alanine.