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The adsorption rate of sodium dodecylbenzenesulfonate (SDBS) on three commercial activated carbons (ACs) and an AC synthesized from almond shells was investigated in this study. The mechanisms controlling the overall adsorption rate of SDBS on ACs were found out by using the pore volume and surface diffusion model (PVSDM). The PVSDM showed that the intraparticle diffusion of SDBS in all ACs was mainly attributed to pore volume diffusion and surface diffusion. The surface diffusion coefficient, Ds, in all samples of ACs are influenced by the amount of surfactant adsorbed at equilibrium, qe, as well as the mean micropore width, L0. The contribution of surface diffusion to the overall intraparticle diffusion ranged from 45 to 70%, depending on the properties of AC. Moreover, the branched-pore diffusional model was revisited (BPDMR) assuming that the Fick diffusion is the only diffusion mechanism in the macropores and the diffusion in the micropores was represented by the micropore rate coefficient, KC. Besides, it was proposed that the parameter f representing the mass fraction of SDBS adsorbed on macropores, can be estimated from the textural properties of ACs. Three new strategies were proposed to analyze the experimental data using BPDMR model, and it was demonstrated that the macropore diffusivity in BPDMR is close to the molecular diffusivity of SDBS in water solution. The micropore rate constant, KC, ranged from 3.90 × 10−6 to 10.6 × 10−6 s−1 and was affected by textural characteristics of ACs. Both models predicted the global adsorption rate of SDBS on ACs satisfactorily. [ABSTRACT FROM AUTHOR]

In this work, a surface diffusion model (SDM) obtained in a previous work was verified in a wide range of experimental conditions to predict the adsorption kinetics of pyridine on activated carbon. Moreover, the predictions of SDM model were compared with that obtained by using the first-order kinetic model. The results showed that the first-order model adjusted satisfactorily the experimental data. The effect of the stirring speed, mass of pyridine adsorbed, (qe), and temperature on the rate constant of the first-order model, (k1), was analyzed and equations were proposed to correlatek1as functions ofqeand temperature. Nevertheless, the dependence ofk1regarding the temperature, stirring speed, andqecannot be accurately correlated, indicating that the overall adsorption rate of pyridine on activated carbon is controlled by the intraparticle diffusion. Moreover, it was shown that the rate of adsorption on active site is not controlling the overall adsorption rate. On the other hand, the SDM model provided a much better prediction than the first-order kinetic model. The surface diffusion coefficient can be readily estimated from a correlation recommended in this work, whereas the value ofk1could not be predicted for some of the experimental conditions studied in this work. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Results obtained demonstrate UV radiation to be unable to degrade RR. [•] Sulfate radicals have a greater selectivity to degrade the RR molecule in comparison to HO radicals. [•] A greater reduction in TOC60 by radicals in ultrapure water and by HO radicals in natural waters. [•] The toxicity of degradation by-products largely depends on the process used. [Copyright &y& Elsevier]

This study analyzed the photocatalytic degradation of cytarabine in the presence of both TiO2 and activated carbon. Three commercial activated carbons denominated as S, M, and W were used in this study. Activated carbon W was oxidized with H2O2, HNO3, or O3. The presence of non-oxidized (S, M, and W) and oxidized (WH2O2, WHNO3, WO3-30, WO3-120) activated carbon enhanced the degradation of cytarabine. The improvement with activated carbons S, M, and W was mainly attributable to their high adsorption capacity of cytarabine, whereas the improvement with activated carbons WH2O2, WHNO3, WO3-30 and WO3-120 was mainly due to interactions between acid sites of the carbons and the radical species generated from the TiO2 photoactivation. Activated carbon samples oxidized with ozone (WO3-30 and WO3-120) had more acid groups on their surface and yielded 20% and 32% additional degradation percentage of cytarabine, respectively. The presence of radical scavengers such as thiourea, t-butanol, and nitrate ions demonstrated that the interactions of HOꔷ and eaq− radicals with acid sites of the activated carbons are responsible for the increased photocatalytic activity of TiO2. The interaction between eaq− and superficial carboxylic acids present on oxidized carbons produced the reduction of carboxylic acids to ketones generating H2O2 which can be decomposed into HOꔷ radicals and, subsequently, the ketones generated can be transformed into an alcoholic superficial group generating additional HOꔷ radicals. [Copyright &y& Elsevier]

The objective of this study was to photocatalytically degrade the pesticide 2,4-dichlorophenoxyacetic acid (2,4-D) by using the integrated UV/TiO2/activated carbon system and to study the degradation kinetics and the role of the chemical and textural properties of activated carbon in this process. Results obtained show that the presence of activated carbon during the catalytic photodegradation (UV/TiO2) of 2,4-D considerably increases its percentage removal. After 60 min of treatment, the highest percentage 2,4-D degradation is obtained in the presence of the activated carbons with the greatest content of carboxyl groups. In order to determine the role of activated carbon in this process, we determined the adsorptive and photocatalytic contribution (UV/TiO2) to the overall 2,4-D removal. The total percentage removal by the UV/TiO2/activated carbon system is much higher than the value obtained by summing the adsorptive and catalytic contributions, mainly when the carbon has an elevated carboxyl group content. No relationship was observed between the textural properties of activated carbons and their synergistic activity; however, the carbons with the greatest carboxyl group content showed the highest synergistic activity. Together with the results of chemical and superficial characterization of the carbon samples after their utilization in the photocatalytic process (UV/TiO2), these findings demonstrate that the reduction of superficial carboxyl groups to alcohol groups is the main pathway by which activated carbon enhances the additional generation of HOꔷ radicals in the medium. Experiments conducted in the presence of radical scavengers (carbonate ions, sulfate ions, and t-butanol) revealed that Hꔷ, eaq−, and HOꔷ species participate in the 2,4-D photodegradation. According to the time course of total organic carbon and toxicity during 2,4-D photodegradation, its complete mineralization is not achieved, and the toxicity of the degradation compounds is lower than that of 2,4-D. [ABSTRACT FROM AUTHOR]

In the present research, the presence of water hyacinth (Eichhornia crassipes) on the surface of the San Jose Dam located in the city of San Luis Potosi, S.L.P, Mexico, was monitored and mapped. The monitoring was conducted for 2 years (2018-2020) with remote sensing data from OLI Landsat 8 sensors, based on the normalized difference vegetation index (NDVI). The results demonstrated the capability and accuracy of this method, where it was observed that the aboveground cover area, proliferation, and distribution of water hyacinth are influenced by climatic and anthropogenic factors during the four seasons of the year. As part of a sustainable environmental control of this invasive species, the use of water hyacinth (WH) root (RO), stem (ST), and leaf (LE) components as adsorbent material for Pb(II) present in aqueous solution was proposed. The maximum adsorption capacity was observed at pH 5 and 25 °C and was 107.3, 136.8, and 120.8 mg g -1 for RO, ST, and LE, respectively. The physicochemical characterization of WH consisted of scanning electron microscopy (SEM), N 2 physisorption, infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), charge distribution, and zero charge point (pH PZC ). Due to the chemical nature of WH, several Pb(II) adsorption mechanisms were proposed such as electrostatic attractions, ion exchange, microprecipitation, and π-cation., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

In this study, the effect of the cell density of monolithic catalysts was investigated and further mathematically modeled on cordierite supports used in CO 2 methanation. Commercial cordierite monoliths with 200, 400, and 500 cpsi cell densities were coated by immersion into an ethanolic suspension of Ni/CeO 2 active phase. SEM-EDS analysis confirmed that, owing to the low porosity of cordierite (surface area < 1 m 2  g -1 ), the Ni/CeO 2 diffusion into the walls was limited, especially in the case of low and intermediate cell density monoliths; thus, active phase was predominantly loaded onto the channels' external surface. Nevertheless, despite the larger exposed surface area in the monolith with high cell density, which would allow for better distribution and accessibility of Ni/CeO 2 , its higher macro-pore volume resulted in some introduction of the active phase into the walls. As a result, the catalytic evaluation showed that it was more influenced by increments in volumetric flow rates. The low cell density monolith displayed diffusional control at flow rates below 500 mL min -1 . In contrast, intermediate and high cell density monoliths presented this behavior up to 300 mL min -1 . These findings suggest that the interaction reactants-catalyst is considerably more affected by a forced non-uniform flow when increasing the injection rate. This condition reduced the transport of reactants and products within the catalyst channels and, in turn, increased the minimum temperature required for the reaction. Moreover, a slight diminution of selectivity to CH 4 was observed and ascribed to the possible formation of hot spots that activate the reverse water-gas shift reaction. Finally, a mathematical model based on fundamental momentum and mass transfer equations coupled with the kinetics of CO 2 methanation was successfully derived and solved to analyze the fluid dynamics of the monolithic support. The results showed a radial profile with maximum fluid velocity located at the center of the channel. A reactive zone close to the inlet was obtained, and maximum methane production (4.5 mol m -3 ) throughout the monolith was attained at 350 °C. Then, linear streamlines of the chemical species were developed along the channel., (© 2024. The Author(s).)

This study investigated the application of adsorption with activated carbons (ACs) and photodegradation to reduce the concentration of triclosan (TCS) in aqueous solutions. Concerning adsorption, ACs (Darco, Norit, and F400) were characterised and batch experiments were performed to elucidate the effect of pH on equilibrium. The results showed that at pH = 7, the maximum adsorption capacity of TCS onto the ACs was 18.5 mg g -1 for Darco, 16.0 mg g -1 for Norit, and 15.5 mg g -1 for F400. The diffusional kinetic model allowed an adequate interpretation of the experimental data. The effective diffusivity varied and increased with the amount of TCS adsorbed, from 1.06 to 1.68 × 10 -8  cm 2  s -1 . In the case of photodegradation, it was possible to ensure that the triclosan molecule was sensitive to UV light of 254 nm because the removal was over 80 % using UV light. The removal of TCS increased in the presence of sulfate radicals. It was possible to identify 2,4-dichlorophenol as one of the photolytic degradation products of triclosan, which does not represent an environmental hazard at low concentrations of triclosan in water. These results confirm that the use of AC Darco, Norit, and F400 and that photodegradation processes with UV light and persulfate radicals are effective in removing TCS from water, reaching concentration levels that do not constitute a risk to human health or environmental hazard. Both methods effectively eliminate pollutants with relatively easy techniques to implement., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)