Jafar Soltan

Breakthrough CO2 adsorption in bio-based activated carbons

In this work, the effects of different methods of activation on CO2 adsorption performance of activated carbon were studied. Activated carbons were prepared from biochar, obtained from fast pyrolysis of white wood, using three different activation methods of steam activation, CO2 activation and Potassium hydroxide (KOH) activation. CO2 adsorption behavior of the produced activated carbons was studied in a fixed-bed reactor set-up at atmospheric pressure, temperature range of 25-65°C and inlet CO2 concentration range of 10-30 mol% in He to determine the effects of the surface area, porosity and surface chemistry on adsorption capacity of the samples. Characterization of the micropore and mesopore texture was carried out using N2 and CO2 adsorption at 77 and 273 K, respectively. Central composite design was used to evaluate the combined effects of temperature and concentration of CO2 on the adsorption behavior of the adsorbents. The KOH activated carbon with a total micropore volume of 0.62 cm(3)/g and surface area of 1400 m(2)/g had the highest CO2 adsorption capacity of 1.8 mol/kg due to its microporous structure and high surface area under the optimized experimental conditions of 30 mol% CO2 and 25°C. The performance of the adsorbents in multi-cyclic adsorption process was also assessed and the adsorption capacity of KOH and CO2 activated carbons remained remarkably stable after 50 cycles with low temperature (160°C) regeneration.

Catalytic ozonation of 2,4-Dichlorophenoxyacetic acid using alumina in the presence of a radical scavenger

Using a laboratory-scale mixed reactor, the performance of alumina in degrading 2,4-Dichlorophenoxyacetic acid with ozone in the presence of tert-butyl alcohol radical scavenger was studied. The operating variables investigated were the dose of alumina catalyst and solution pH. Results showed that using ozone and alumina leads to a significant increase in 2,4-D removal in comparison to non-catalytic ozonation and adsorption processes. The observed reaction rate constants (kobs ) for 2,4-D during ozonation were found to increase linearly with increasing catalyst dose. At pH 5, the kobs value increased from 19.3 to 26 M−1 s−1 and 67 M−1 s−1 when varying the alumina dose from 1 to 2 and 4 g L−1, respectively. As pH was increased, higher reaction rates were observed for both non-catalytic ozonation and catalytic ozonation processes. Thus, at pH 3 and using a catalyst dose of 8 g L−1, the kobs values for non-catalytic ozonation and catalytic ozonation processes were 3.4 and 58.9 M−1 s−1, respectively, whereas at pH 5 reaction rate constants of 6.5 and 128.5 M−1 s−1 were observed, respectively. Analysis of total organic carbon suggested that catalytic ozonation with alumina achieved a considerable level of mineralization of 2,4-D. Adsorption of 2,4-D on alumina was found to play an important role in the catalytic ozonation process.

Adsorption of emerging pollutants on activated carbon

Abstract Many emerging pollutants (also known as micro-pollutants) including pesticides, pharmaceutical and personal care products (PPCPs), and endocrine disrupting chemicals (EDCs) have frequently been detected in surface, ground, and drinking water at alarming concentrations. The emission and accumulation of these anthropogenic chemicals in nature is a potential threat to human health and aquatic environment. Therefore, it is essential to devise an effective and feasible technology to remove the micro-pollutants from water. Activated carbon adsorption has been introduced and utilized as a promising treatment to reduce the concentration of the emerging pollutants in water. A summary of research on the removal of pesticides, PPCPs, and EDCs by activated carbon adsorption process is presented in this report. The effects of carbon characteristics, adsorptive properties, and environmental factors on the adsorption capacity of activated carbon are reviewed. In addition, the mechanisms of the adsorption including hydrophobicity and the nature of the functional groups of activated carbon and organic compounds are discussed. Furthermore, the applied equilibrium adsorption isotherms (Langmuir, Freundlich, BET, Sips, Dubinin-Astakhov, Dubinin-Radushkevich, and Toth) and the most common kinetic models (pseudo-first- and second-order models, film and intra-particle diffusion models, and adsorption-desorption model) are also included for further investigation. This comprehensive review report aims to identify the knowledge deficiencies regarding emerging pollutant treatment via activated carbon adsorption process and open new horizons for the future research on the adsorption of emerging pollutants on activated carbon.

Ultrasonic degradation of 1-H-benzotriazole in water.

This paper reports on the effect of different parameters of ultrasonic power, pollutant initial concentration, pH and the presence of co-existing chemical species (oxygen, nitrogen, ozone, and radical scavengers) on the ultrasonic degradation of the endocrine disruptor 1-H-benzotriazole. Increasing the 1-H-benzotriazole initial concentration from 41.97 to 167.88 μM increased the pollutant degradation rate by 40%. Likewise, a high applied ultrasonic power enhanced the extent of 1-H-benzotriazole removal and its initial degradation rate, which was accelerated in the presence of ozone and oxygen, but inhibited by nitrogen. The most favorable pH for the ultrasonic degradation was acidic media, reaching ∼90% pollutant removal in 2 h. The hydroxyl free radical concentration in the reaction medium was proportional to the ultrasound power and the irradiation time. Kinetic models based on a Langmuir-type mechanism were used to predict the pollutant sonochemical degradation. It was concluded that degradation takes place at both the bubble-liquid interfacial region and in the bulk solution, and OH radicals were the main species responsible for the reaction. Hydroxyl free radicals were generated by water pyrolysis and then diffused into the interfacial region and the bulk solution where most of the solute molecules were present.

Role of Surface Carboxylates in the Gas Phase Ozone-Assisted Catalytic Oxidation of Toluene

Ozone-assisted catalytic oxidation of toluene was conducted over MnOx/γ-Al2O3 to identify and differentiate the role of reaction byproducts. It was found that not only alumina acted as a reservoir for toluene, but also it interacted effectively with toluene to create surface carboxylate intermediates. Surface carboxylates were essential for an effective oxidation process, and they did not directly cause catalyst deactivation. The presence of Mn sites was necessary for further oxidation of the surface carboxylates. At 90 °C, a stable catalytic activity with 95% conversion was achieved. However, at 25 °C, byproducts such as acetic acid and formic acid accumulated on the surface of the catalyst and decreased the catalyst activity.Graphical Abstract

Mineralization of Ibuprofen and Humic Acid through Catalytic Ozonation

ABSTRACT Advanced oxidation methods are used to remove traces of pharmaceuticals from aquatic environments. The application of a catalyst improves the total organic carbon removal during ozonation of pharmaceuticals in water. The aim of this study was to use MnO2-CuO/ γ-Al2O3 catalyst for ozonation of ibuprofen (5 mgL−1) and evaluate the effect of the presence of humic acid in the removal process. The presence of the catalyst increased the mineralization percentage of ibuprofen from 27% for noncatalytic ozonation to 55% in the presence of catalyst. The presence of humic acid increased noncatalytic mineralization by 10%. The reusability and stability of the catalyst, and its ability to adsorb reaction by-products were demonstrated.

Sonochemical degradation of triclosan in water in a multifrequency reactor

Degradation of triclosan (TCS) by multifrequency ultrasound (US) was studied at high and low frequencies. Frequency effect on initial degradation rates was analyzed, and an optimum frequency was found. Power density always has a positive effect on degradation rates over the whole equipment work range. A reaction mechanism similar to that proposed by Serpone resulted in a pseudo-linear model that fitted statistically better than the nonlinear model proposed by Okitsu. Pulsed US showed a positive effect on degradation rates; however, simultaneous analysis of the effect of power, frequency, pulse time, and silent time did not show a clear trend for degradation as a function of pulse US variables. According to these results and those for degradation in the presence of radical scavengers, it was concluded that US TCS degradation was taking place in the bubble/liquid interface. A toxicity test was conducted by Microtox®, showing a decrease in toxicity as TCS concentration decreased and increase in toxicity after total depletion of TCS. Eight possible degradation by-products were identified by GC-MS analysis, and a degradation pathway was proposed.

Iron Catalysts Supported On Carbon NanotubesFor Fischer–Tropsch Synthesis:Effect Of Pore Size

In this report, the effects of pore diameter and structure of iron catalysts supported on carbon nanotubes (CNTs) on Fischer–Tropsch (FT) reaction rates and product selectivities are presented. Two types of CNTs with different average pore sizes (12 and 63 nm) were prepared. The CNTs were chosen in a way to have comparable surface areas so as to eliminate the effects of different surface areas. The iron catalysts (the narrow pore catalyst denoted Fe/np-CNT and wide pore catalyst denoted Fe/wp-CNT) were prepared using incipient wetness impregnation method and characterized by ICP, BET, XRD, TPR, SEM and TEM analyses. The TEM and XRD analysis showed that the iron oxide particles on the Fe/wp-CNT (17 nm) were larger than those on Fe/np-CNT sample (11 nm). TPR analyses of the catalysts showed that the degree of reduction of the Fe/np-CNT catalyst was 17% higher compared to that of the Fe/wp-CNT catalyst. For the FT reactions, it was found that the activity of the np-CNT catalyst (%CO conversion of 31) was much higher than that of the wpCNT catalyst (%CO conversion of 11). Also, the Fe/wp-CNT was more selective toward lighter hydrocarbons with a methane selectivity of 41% whereas, the methane selectivity of the np-CNT catalyst was 14%. It can be concluded that the deposition of the metal particles on the CNT with narrow pore size (in the range of larger than 10 nm) results in more active and selective catalyst due to higher degree of reduction and higher metal dispersion.