Apparent Kinetic Model Research Articles

Track of methylparaben in the bulk phase and on the extracellular matrix of dual-species biofilms: Biodegradation and bioaccumulation

Methylparaben (MP) is a preservative considered an environmental contaminant of emerging concern due to its persistence in water sources, including drinking water (DW). This study assesses the interaction between MP and dual-species biofilms of Acinetobacter calcoaceticus and Stenotrophomonas maltophilia. These biofilms were grown under realism-based conditions in a multiple-cylinder biofilm reactor on polypropylene (PPL) surfaces, for 7 days, and then exposed to MP at 0.5 mg/L for three consecutive days. S. maltophilia predominantly succeeds within these biofilms compared to A. calcoaceticus. Exposure to MP resulted in a 4-fold increase in the number of culturable cells and a 1.4-fold rise in polysaccharide content, suggesting that bacterial cells may utilize MP as a carbon source to enhance biofilm fitness. MP was found to adsorb to PPL with biofilms following a pseudo-second-order kinetic model. Circa 37 % of MP adsorbed to PPL after 3 days of exposure. Besides that, MP was biodegraded by biofilms following an apparent first-order kinetic model. Part (25 %) of the MP was biodegraded whereas only 0.02 % bioaccumulated on the biofilm matrix. Biodegradation was related to esterase and lipase activity. The results provide new insights into the interaction between MP with biofilms and materials used in DW industries.

Kinetic modeling of methane dehydroaromatization over Mo/ZSM-5 catalysts

We propose a novel kinetic model for the methane dehydroaromatization (MDA) reaction over the Mo/ZSM-5 catalyst to express the practical behavior of the catalytic reaction. Unlike existing MDA kinetic models, we introduced a deactivation model involving carbon deposit formation to simulate the more realistic behavior of the MDA reaction. The proposed kinetic model integrated the “apparent kinetic model,” which focuses on detectable components, and the “micro-kinetic model,” which incorporates the acidic properties and active sites of the catalyst. To validate this model, we conducted fixed-bed experiments across a wide range of operating conditions, including temperature, gas velocity, and metal loading. Compared with experimental data, our model predictions exhibited a remarkable error of 5 %. Specifically, by leveraging the relationship between the deactivation behavior and carbon deposit formation, the model accurately predicted the CH4 conversion rates, component yields, and coke production throughout the reaction. This model sheds light on catalytic behavior during carbon deposit generation under diverse operating conditions, contributing to a comprehensive understanding of the MDA reaction mechanism. The developed kinetic model can be applied to estimate reactor performance across various scenarios. By providing a kinetic model that incorporates information regarding the catalytic properties of Mo/ZSM-5 and the apparent gas concentration, our study offers a potent tool for estimating practical reactor performance and advancing MDA catalyst development.

Synthesis, characterization, and photocatalytic properties of reed biochar/TiO2 composites

In this study, TiO2/biochar (TBC) materials were successfully synthesized by simple hydrolysis. The photocatalytic activity of the products was evaluated through the photodegradation ability of doxycycline (DC) in aqueous solution. Characterization shows that TiO2 nanoparticles are well dispersed on the biochar surface. The presence of biochar helped improve the specific surface area, narrow the band gap and enhance the optical absorption in the visible light region of TiO2. The TBC composite at TiO2/biochar mass ratio = 1/0.25 showed the highest photodegradation efficiency, about 3.77 times higher than pure TiO2. Kinetic studies showed that DC degradation followed an apparent first-order kinetic model with rate constant kapp = 2.66×10-2 min-1 at DC concentration of 7.0 mg/L. Research shows that TiO2/biochar material has great potential for treating antibiotic-contaminated wastewater.

A Study on the Pyrolysis Behavior and Product Evolution of Typical Wood Biomass to Hydrogen-Rich Gas Catalyzed by the Ni-Fe/HZSM-5 Catalyst

The thermo-chemical conversion of biomass wastes is a practical approach for the value-added reclamation of bioenergy in large quantities, and pyrolysis plays a core role in this process. In this work, poplar (PR) and cedar (CR) were used as staple wood biomasses to investigate the apparent kinetics of TG/DTG at different heating rates. Secondly, miscellaneous wood chips (MWC), in which PR and CR were mixed in equal proportion, were subjected to comprehensive investigations on their pyrolysis behavior and product evolution in a fixed bed reactor with pyrolysis temperature, catalyst, and the flow rate H2O steam as influencing factors. The results demonstrated that both PR and CR underwent three consecutive pyrolysis stages, the TG/DTG curves shifted to higher temperatures, and the peak temperature intervals also enhanced as the heating rate increased. The kinetic compensation effect expression and apparent reaction kinetic model of CR and PR pyrolysis were obtained based on the law of mass action and the Arrhenius equation; the reaction kinetic parameter averages of Ea and A of its were almost the same, which were about 72.38 kJ/mol and 72.36 kJ/mol and 1147.11 min−1 and 1144.39 min−1, respectively. The high temperature was beneficial for the promotion of the pyrolysis of biomass, increased pyrolysis gas yield, and reduced tar yield. This process was strengthened in the presence of the catalyst, thus significantly increasing the yield of hydrogen-rich gas to 117.9 mL/g-biomass. It was observed that H2O steam was the most effective activator for providing a hydrogen source for the whole reaction process, promoted the reaction to proceed in the opposite direction of H2O steam participation, and was beneficial to the production of H2 and other hydrocarbons. In particular, when the flow rate of H2O steam was 1 mL/min, the gas yield and hydrogen conversion were 76.94% and 15.90%, and the H2/CO was 2.07. The yields of H2, CO, and CO2 in the gas formation were significantly increased to 107.35 mL/g-biomass, 53.70 mL/g-biomass, and 99.31 mL/g-biomass, respectively. Therefore, H2 was the most dominant species among gas products, followed by C-O bond-containing species, which provides a method for the production of hydrogen-rich gas and also provides ideas for compensating or partially replacing the fossil raw material for hydrogen production.

Apparent kinetics and thermodynamics study of methyl ethyl ketone peroxide in efficient continuous-flow microreaction system and its kiloton pilot plant

Organic peroxides are vital fine chemicals, and methyl ethyl ketone peroxide (MEKPO) is the most typical and commonly used one. However, the organic peroxide industry is highly hindered by frequent accidents resulting from their synthetic reaction. It's significant demand for green advances to develop efficient & safe synthesis technology for MEKPO and other organic peroxides. Moreover, lacking quantitative model for MEKPO, it's insufficient to determine regulatory mechanism, eliminate potential risks, and achieve successful scale-up. Herein, a microreaction platform was established to uncover thermodynamic constant and apparent kinetics model of MEKPO synthesis. Under its guidance, the microreaction process was scaled-up to 1000 tons/year productivity. In the pilot plant, the conversion is higher than batch process, within only 390 s residence time. The space-time yield increased by 55 times, which greatly reduced liquid hold-up and ensured safety. It's the first microreaction pilot plant for organic peroxides, improving both safety and efficiency for the industry.

Synthesis of hierarchical FePc-ZS-1 zeolites and its rapid photocatalytic degradation of MB under visible light and H2O2

This manuscript details the successful production of hierarchical FePc-ZS-1 zeolite with rapid visible photocatalytic properties through an impregnation method utilizing reactive dyes as a sensitizing agent. The impact of the dye species on the visible photocatalytic properties of the resulting products was thoroughly examined in a Fenton reaction system created by combining H2O2 and the synthesized materials. The synthesized materials were subjected to characterization through various methods including XPS, XRD, FTIR, SEM, and N2 adsorption-desorption isotherm.The synthetized FePc-ZS-1 zeolite is an ellipsoid with smooth surface, highly ordered pore structure, and characteristic peaks in the visible region of 400–800 nm. The final results indicate that the phthalocyanine dye-sensitized zeolite had the most significant impact on the visible light degradation efficiency of methylene blue dye solution. The degradation efficiency of FePc-ZS-1 zeolite on MB solution reached an amazing 99.96 % in just 30 min. After examining the photocatalytic activity and kinetics model, it was determined that the photocatalytic activity is consistent with the apparent first-order kinetic model. Furthermore, through radical capture experiments and ESR characterization, the hypothesized mechanism of the photocatalytic reaction and the MB degradation pathways were thoroughly addressed. Finally, the samples were subjected to reuse experiments, and the results showed that the degradation rate was still above 90 % after 5 times of reuse, with good recyclability. The above results indicate that the visible photocatalytic material prepared in this study is a promising source of green energy, which is worthy of further application.

Limestone hydrogenation combined with reverse water–gas shift reaction under fluidized and iso-thermal conditions using MFB-TGA-MS

The integrated CO2 capture and utilization (ICCU) in conjunction with the reverse water–gas shift (RWGS) reaction has emerged as a promising approach to achieve carbon neutrality. However, the scalability of CaCO3 hydrogenation in the context of large volumes of industrial flue gas is impeded by the limited understanding of its performance under fluidized and iso-thermal conditions. This study utilized micro-fluidized bed thermogravimetric analysis coupled with mass spectrometry (MFB-TGA-MS) and in-situ measurements to investigate limestone decomposition under H2 and Ar atmospheres. Results showed that H2 atmosphere increased the limestone decomposition rate by 5-fold (79.1% CO2 conversion and ∼100% CO selectivity at 710 °C) compared to Ar, with RWGS as the dominant route and self-catalytic activity of calcined CaO. Morphology evolution revealed finer pores and textures under H2 conditions. Meanwhile, apparent kinetic models analyzed experimental data and showed a reduction in activation energy from 178.5 kJ/mol (Ar) to 161.3 kJ/mol (H2). These findings support the effectiveness of ICCU-RWGS approaches for further commercialization.

Kinetics of glyoxal oxidation by nitric acid in a capillary microreactor

Aiming at solving the problems of long operation periods, low selectivity, and low safety in the traditional batch reactor, a method of oxidation reaction of glyoxal with nitric acid through a continuous flow microreactor is proposed, with high selectivity. The method utilizes the excellent performance of mass and heat transfer in the microreactor, to improve the reaction efficiency, selectivity, and safety. The effects of the mixing performance, the molar ratio of reactants, temperature, residence time, and mass fraction of nitric acid on the oxidation of glyoxal with nitric acid are investigated, and the optimum reaction conditions are determined. The glyoxylic acid yield can reach 81.6% while the selectivity is 92.4% with the set residence time of only 7.9 min at 68 ℃ (the molar ratio of nitric acid to glyoxal is 1.4, sodium nitrite to glyoxal is 0.15, hydrochloric acid to glyoxal is 0.2, and the mass concentration of nitric acid is 35%). The apparent kinetic model of the oxidation reaction of glyoxal with nitric acid in a microchannel reactor is established. By precisely controlling the reaction temperature and residence time of the continuous flow microreactor system, the apparent reaction rate constants, pre-exponential factor, and activation energy of glyoxal oxidation to glyoxylic acid by nitric acid are obtained. This work paves the way for the promotion of the synthesis of glyoxylic acid in a microreactor by the continuous flow chemistry system.

Kinetics of coupled sorption and abiotic oxidation of antimony(III) in soils

A quantitative evaluation of the dynamics of antimony (Sb) species transformation when Sb(III) enters the soil matrix would facilitate the understanding of the speciation and environmental fate of Sb in natural environments. Towards this end, the coupled sorption and abiotic oxidation kinetics of Sb(III) were examined across 12 soils with a 24 h timeframe. The soil-solution distribution coefficients (Kd) of Sb ranged between 214 and 5965 L kg−1. Both apparent and mechanistic kinetic models were used to described the process. The apparent kinetic model indicated a two-rate oxidation and associated stabilization behavior of Sb in soils. The fast oxidation rate constants ranged from 0.147 to 0.763 h−1, which were one to two orders of magnitudes higher than the slow rate constants (0.002–0.039 h−1). Iron and Mn oxides were identified as the key soil components associated with adsorptive-oxidative sites (SOH) and oxidative sites (Mn-OH) of soils for Sb species, and these were subsequently integrated into the mechanistic kinetic model. This model included the adsorption–desorption of Sb(III) as well as the oxidation product, Sb(V) on the SOH, the oxidation of Sb(III) by SOH and Mn-OH, and the stabilization of both Sb(III) and Sb(V). The model produced a global fit for dissolved and adsorbed Sb species across the 12 soils. This study provides new information for predicting the dynamics of Sb in soils when multiple adsorption–desorption, oxidation and stabilization reactions are coupled in natural environments.

Hydrosilylation of alkenes with tertiary silanes under mild conditions by Pt(II)-vinyl complex supported on modified rice straw biochar

Alkylsilanes, obtained from hydrosilylation of alkenes with tertiary silane, have high commercial application value. It is crucial to develop a heterogeneous Pt-based catalyst with high activity and high regioselectivity to catalyze this hydrosilylation reaction under solvent-free and mild conditions. Herein, a stable Pt(II)-vinyl complex with unique structure was successfully constructed on oxidized rice straw biochar through reasonable structural design and modification steps. Pt particles on the as-prepared catalyst (Pt-VTES-RSOC) were evenly dispersed with relatively minimum particle sizes (0.3∼2.5 nm). Compared to classic homogeneous catalysts, Pt-VTES-RSOC showed superior activity, great regioselectivity for tertiary silanes and high reusability. The apparent kinetic models for representative reactions over Pt-VTES-RSOC were also proposed to simulate the catalytic process under suggested reaction conditions for clarifying the reaction mechanism. The study proved that Pt-VTES-RSOC would have a good industrial application potential in hydrosilylation of alkenes with tertiary silanes by reducing operation cost and increasing the product quality.

High Temperature CO2 Capture Performance and Kinetic Analysis of Novel Potassium Stannate.

For the first time, the use of stannate-based sorbents was investigated as high temperature CO2 sorption to evaluate their potential to contribute towards reducing carbon emissions. The sorption capacity and kinetics of commercial tin oxide, sodium, potassium and calcium stannates and lab synthesised potassium stannates were tested using thermogravimetric analysis. Commercial K2SnO3 was found to possess the largest CO2 uptake capacity (2.77 mmol CO2/g or 12.2 wt%) at 700 °C, which is among the highest for potassium sorbents, but the CO2 desorption was not successful. On the contrary, the in-house synthesised K-stannate (K-B) using facile solid-state synthesis outperformed the other sorbents, resulting in a CO2 uptake of 7.3 wt% after 5 min, an adsorption rate (0.016 mg/s) one order of magnitude higher than the other stannates, and stability after 40 cycles. The XRD and XPS analyses showed that K-B contains a mixture of K2SnO3 (76%) and K4SnO4 (21%), while the Scherrer crystal sizes confirmed good resistance to sintering for the potassium stannates. Among the apparent kinetic model tested, the pseudo-second order model was the most suitable to predict the CO2 sorption process of K-B, indicating that chemical adsorption is dominant, while film-diffusion resistance and intra-particle diffusion resistance governed the sorption process in K-B. In summary, this work shows that solid-state synthesised potassium stannate could be an effective sorbent for high temperature separation, and additional work is required to further elucidate its potential.

Cefotaxime degradation by the coupled binary CdS-PbS: characterization and the photocatalytic process kinetics.

Increased water pollution due to discharging industrial/urban/hospital wastewater has been adopted to introduce/develop novel removal techniques/catalyst/adsorbent. The hexagonal (wurtzite) CdS and the cubic PbS nanoparticles (NPs) were synthesized, coupled, and supported onto clinoptilolite NPs (CNP). Then, the sample was characterized by X-ray powder diffraction (XRD), diffuse reflectance spectroscopy (DRS), Fourier transform infrared (FTIR), and a scanning electron microscope equipped with an energy dispersive X-ray analyzer (SEM-EDX) techniques. The average crystallite size for CdS NPs, PbS NPs, CNP, and CdS-PbS/CNP samples was obtained at about 24, 36, 27, and 14nm using the Scherrer formula value of nanometer, by the W-H formula, 31, 17, 39, and 51, respectively. Only a detectable slope can be observed from the DRS spectra for CdS NPs at 591nm corresponding to an Eg value of 2.1eV. PbS NPs have a broad abruption peak that begins from the visible region and extends to the IR region of the light. A boosted photocatalytic activity of the supported binary catalysts towards cefotaxime (CT) was reached. An apparent first kinetic model was reached with a k-value of 0.021min-1 corresponding to the t1/2 value of 33min. A decreased COD trend for the photodegraded CT solutions was reached, and the chemical oxygen demand (COD) results in the Hinshelwood model showed a k-value of 0.016min-1, corresponding to a t1/2 value of 43min.

Kinetics and Activation Complex Thermodynamic Study of the Acidity Removal of Oleic Acid via Esterification Reaction on Commercial 13X Zeolite

The study involved the removal of acidity from free fatty acid via the esterification reaction of oleic acid with ethanol. The reaction was done in a batch reactor using commercial 13X zeolite as a catalyst. The effects of temperatures (40 to 70 °C) and reaction time (up to 120 minutes) were studied using 6:1 mole ratio of pure ethanol to oleic acid and 5 wt. % of the catalyst. The results showed that acid removed increased with increasing temperature and reaction time. Also, the acidity removal rises sharply during the first reaction period and then changes slightly afterward. The highest acidity removal value was 67 % recorded at 110 minutes and 70 °C. An apparent homogeneous reversible reaction kinetic model has been proposed and solved with the experimentally obtained kinetics data to evaluate reaction rate constants versus temperature, pre-exponential factors, and activation energy values for the forward and the backward esterification reactions. The activation energies were 34.863 kJ/mol for the forward reaction and 29.731 kJ/mol for the backward reaction. The thermodynamics of the activation step of the forward and reverse reactions was studied based on the hypothesis of forming a complex material that decomposes into a product. The activation steps were studied using Eyring bimolecular collision theory approach, and both ΔH* and ΔS* were determined for forward and backward esterification reactions. The enthalpies of activation were 32.141 kJ/mol and 27.080 kJ/mol for the forward reaction and the backward reaction, and the entropies of activation were - 193.7 and -212.7 J/mol. K for the forward reaction and the backward reaction, respectively.

A novel approach for removing cadmium from synthetic wet phosphoric acid using sulfide precipitation process operating in batch and continuous modes

The removal of heavy metals, especially cadmium, from wet phosphoric acid is still a challenging stage during the manufacturing of phosphate fertilizers. In this work, a novel approach was developed to improve the performance of the sulfide precipitation process as a purification technique. This is based on NaHS rather than Na2S as a precipitating agent in both batch and continuous modes for cadmium removal from synthetic wet phosphoric acid. First, the respective performance of Na2S and NaHS was compared in the batch mode. NaHS was shown to improve decadmiation in comparison to Na2S even though the same trends were observed for both precipitating agents as a function of operating conditions. An increase in Sulfur/Cd2+ molar ratio improved cadmium sulfide precipitation. Conversely, increasing temperature and phosphoric acid concentration impaired the effectiveness of cadmium removal efficiency. An apparent kinetic model was developed taking into consideration the reaction mechanisms and supersaturation to predict the residual cadmium concentration in phosphoric acid solutions. The feasibility of the continuous process based on NaHS was also assessed. The results showed that a residence time of 40 min was needed to achieve 85.6 % of Cd2+ elimination at 25 °C. As aggregation seemed to be the main mechanism governing particle size, this increased with the Sulfur/Cd2+ ratio, which could improve downstream solid separation. Eventually, these findings of this study provide useful insights into the feasibility of chemical precipitation using NaHS as a technology of phosphoric acid decadmiation in the industry.

Continuous flow nitration of 3-[2-chloro-4-(trifluoromethyl) phenoxy] benzoic acid and its chemical kinetics within droplet-based microreactors

• The synthesis of Acifluorfen by continuous flow nitration was performed within droplet-based microreactor. • The effects of operating parameters were characterized by hydrodynamics and thermodynamics. • The apparent and intrinsic kinetic model was established. Aromatic nitration still faces unmet technical challenges in relation to being heterogeneous and highly exothermic. In this work, a continuous flow aromatic nitration was developed with mixed acid within droplet-based microreactors. The effects of key operating parameters were characterized on the nitration of 3-[2-chloro-4-(trifluoromethyl)phenoxy] benzoic acid. The optimized reaction temperature, M-ratio and N/S were found to be 308 K, 1.6 and 0.57, respectively. Under these conditions, a conversion of 83.03% and selectivity of 79.52% were achieved. The addition of acetic anhydride improved both the solubility of etherate in the organic phase and the absorbability of water produced from the reaction, leading to increase in conversion, however increased by-products accordingly with reduced selectivity. Pseudo-homogeneous kinetics models were developed of apparent and intrinsic reaction rate constant, supporting the second-order reaction assumption. The calculated results based on the kinetics model were found to be in good agreement with the experimental results.

Biogas upgrading with various single and blended amines solutions: Capacities and kinetics

Biogas is an important renewable energy and biogas upgrading which separate CH4/CO2 to increase the heating value of biogas is necessary for its utilization. Amine scrubbing is a promising biogas upgrading technology. In this study, we applied various single and blended amines solutions for biogas upgrading and reconsidered the evaluation method by comparing the equilibrium CO2 absorption capacity (qe) and optimal CO2 absorption capacity under 90 vol% or 95 vol% pure CH4 requirement (q90%CH4, q95%CH4). Three apparent kinetic models and Fourier-transform infrared spectroscopy (FT-IR) were applied to study the kinetics. The results showed that, compared with the qe, the new indicator q90%CH4 and q95%CH4 could better reveal the difference and improvements between various amines solutions and be more accordance with the real situation of biogas upgrading. The q90%CH4 increased from 0.15 to 0.82–1.70 mol/kg after adding other amines with methyldiethanolamine (MDEA), but qe was almost the same. For kinetics, the fitting results of Avrami model are the best among the three models. FT-IR analysis before and after absorption showed CO2 formed different groups with different amine molecules. This study provided a new perspective and method on evaluation of amine scrubbing for biogas upgrading, contributing to future research and industrial application.

An innovative kinetic model allowing insight in the moderate temperature chemical vapor deposition of silicon oxynitride films from tris(dimethylsilyl)amine

An apparent kinetic model is developed for a novel chemical vapor deposition (CVD) process of silicon oxynitride (SiOxNy) films from tris(dimethylsilyl)amine (TDMSA) and O2, operating at moderate temperature (600–650 °C) and at atmospheric pressure. The definition of reaction pathways and the extraction of kinetic information is based on recently reported results of the gas phase composition, complemented by solid phase characteristics obtained by spectroscopic ellipsometry (SE) and ion beam analyses (IBA). Incorporation of carbon (up to 20 at.%) is considered alongside nitrogen (up to 25 at.%) for variable O2 flow rates (0.3–1.2 sccm). This combined gas- and solid-phase analysis is utilized to identify the main gaseous species and provide insight into the deposition mechanism. A silicon- and a nitrogen-centered radical intermediates are considered as the primary species of the mechanism, based on evidence from gas phase characterizations. A third, fictitious, nitrogen- and carbon-containing molecule is also conceptualized to account for carbon incorporation. Eight chemical reactions are defined alongside their respective kinetic parameters and are implemented in the ANSYS® FLUENT® computational fluid dynamics (CFD) code. Upon validation, the model allows for the successful prediction of local deposition rates and SiOxNy film composition containing non-negligible carbon, marking it as the first kinetic model able to represent the main chemical mechanisms involved in the CVD of a four-component material. The reported combined approach could be applied to other existing or new CVD chemistries forming multi-component thin films, favoring their implementation in original applications.

Investigations on the chemical looping with oxygen uncoupling process using Indian coal and copper oxide oxygen carrier

In this study, the effectiveness of CuO as an oxygen carrier (OC) in chemical looping with oxygen uncoupling (CLOU) process was investigated using three Indian coals with varying origin and nature. The thermogravimetric analysis (TGA) experiments were performed with coal to OC mass-ratio of 1:20, 1:30, and 1:40 at varying temperatures of 800, 850, 900, 950 °C. The mass loss profiles of coal/CuO indicated that the CLOU combustion reaction was the most suitable with a mass ratio of 1:30 and at 850 °C. Multicyclic combustion-reoxidation performance (for 45 h) also showed sufficiently good repeatability with minor agglomeration. Besides, the kinetic triplet, such as apparent activation energy (Ea), pre-exponential factor (A), and kinetic model function, g(x), were estimated for reactions in the pyrolysis and combustion zones applying the Coats and Redfern model on the TGA mass loss data. From mathematical model fitting, it was found that the three-dimensional Jander-diffusion model provides an excellent fit to the experimental data for the selected temperature zones, and the combustion reaction kinetics is likely to be a diffusion dominated process. The estimated apparent activation energies for three coals studied in this work were in the range of 38.3–60.1 kJ/mol and 102.6–129.0 kJ/mol in the temperature zone of 400–600 °C and 600–950 °C, respectively. The findings of the present study suggest first-time that the Indian coal-based CLOU process using CuO OC is promising, and the derived kinetic information will be useful for CLOU reactor design using Indian coal and CuO OC.

Ultrafast catalytic reduction of toxic nitroaromatics and organic colouring dyes by using Au/ZIF-11: Efficient wastewater treatment

An ultrafast catalytic method to reduce various toxic nitrophenols, nitroaniline and organic dyes by using gold nanoparticles decorated-ZIF-11 (Au/ZIF-11) composite for wastewater treatment has been described. Three new Au/ZIF-11 composites (abbreviated as Au0.1Z, Au0.2Z and Au0.3Z) have been synthesized via direct reduction of HAuCl4 (0.1 to 0.3 mM) using sodium borohydride (NaBH4) in the suspension of pre-synthesized ZIF-11 and characterized by various spectroscopic and morphological/surface techniques. TEM images confirmed the formation of spherical and uniformly distributed gold NPs, having average particle size of 7.35 ± 0.95 nm, on the surface of ZIF-11 microcrystals. Au0.2Z displayed exceptionally high catalytic efficiency towards the reduction of nitrophenols (2-NPhenol, 3-NPhenol and 4-NPhenol), 4-nitroaniline (4-NANI) and 2,4,6-triNPhenol at substrate's concentration: 1.58 × 10−4 M in the presence of NaBH4 (0.04 M) at ambient condition. k̅app, (apparent rate constant) was (4.64/3.24/1.90) × 10−2 s−1 having activity coefficient k′ (k′ = k̅app/M) value of 928.83, 647.59 and 380.61 s−1 g−1 for 3-NPhenol, 4-NPhenol and 2-NPhenol, respectively, using Au0.2Z ([catalyst] = 15.87 μg/mL). Further, Au0.2Z can be re-used up to 5 cycles with more than 90% conversion efficiency. Moreover, Au0.2Z also reduced organic colouring dyes (methylene blue (MB), rhodamine B (RhB), congo red (CR) and methyl orange (MO)) in the presence of NaBH4 and the corresponding k̅app was 7.88 × 10−3–9.22 × 10−4 s−1 with k′ value of 157.71–9.22 s−1 g−1. The probable mechanism involving Langmuir-Hinshelwood apparent first-order kinetics model described that Au nanoparticles immobilized onto ZIF-11 may serve as antenna to transfer electrons and hydrogen from borohydride (BH4−) ions to the acceptor (nitro group/organic dye). Therefore, Au0.2Z can effectively be used for environmental remediation application to remove organic pollutants from the industrial wastewater.

Adsorption desulfurization performance of PdO/SiO2@graphene oxide hybrid aerogel: Influence of graphene oxide

Preparation of PdO/SiO2@graphene oxide (GO) hybrid aerogels were carried out sol-gel method combined with atmospheric drying technology to study their adsorption performance for thiophenics and compared with PdO/SiO2. Scanning electron microscope (SEM), N2 adsorption-desorption isotherms, X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), and fourier transformation infrared spectroscopy (FT-IR) for samples were performed. The adsorption performance of PdO/SiO2@GO for thiophene were better than that of PdO/SiO2, attributed to that incorporation of GO increased the specific surface area and the Pd incorporation rate, where Pd2+ ions acted as the π-complexation and sulfur-metal (SM) bond adsorption active centers, as well as GO adsorbed thiophene by the π-π stacking effect. The adsorption capacities of PdO/SiO2@GO-1.0 for thiophene (TH), benzothiophene (BT) and dibenzothiophene (DBT) were 8.89, 9.3 and 12.6 mg-S/gads, respectively. The addition of GO in aerogels could improve the inhibition effect of toluene, cyclohexene and pyridine while decreased the inhibition effect of MTBE and H2O for the adsorption of thiophene, due to the π-π stacking effect and the hydrophobicity of GO, respectively. The adsorption process was spontaneous and exothermic, be well fitted by the apparent second-order kinetic model and dominated by chemical interaction. Pd/SiO2@GO-1.0 had a good solvent elution regeneration performance.