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Due to the worldwide concern about emerging contaminants in aqueous systems, the main objective of the present study is the adsorption of gemifloxacin (GMF), a fluoroquinolone‐type antibiotic, by rice straw‐based activated carbon. The rice straw chemically activated with K2CO3 (RSAC) had very high carbon content (>80%) and low silica content (due to the extraction step after activation), high specific surface area (1668 m2/g), and oxygenated functional groups. The GMF adsorption capacity of RSAC was relatively dependent on the initial pH of the solution and highly dependent on the adsorbent dose. The pseudo‐second order model and the BET isotherm models were the best models for predicting adsorption's kinetic and equilibrium behaviors. The maximum monolayer adsorption capacities of RSAC at 25, 35, and 45°C were 565.6, 552.4, and 525.8 mg/g, respectively. The thermodynamic parameters indicated a spontaneous and exothermic character of the GMF adsorption process. n–π, π–π, electrostatic interactions, and hydrogen bonding were demonstrated as probable mechanisms involved. Thermal regeneration of GMF‐saturated RSAC at 550°C resulted in perfect adsorbent regeneration in the second cycle and reasonable performance in the third cycle. [ABSTRACT FROM AUTHOR]

Decreasing the concentration of pollutants in wastewater is a necessary issue particularly in the third-world countries. Mercury is known as one of the most important metal contaminants with harmful impacts on the environment. The present work is based on the lab-scale Hg elimination from synthetic wastewater. For this purpose, adsorption application in continuous mode has been chosen and a modified activated carbon which is sulphurised via dimethyl-disulphide was applied as adsorbent. Thus, the original activated carbon performance in Hg2+ adsorption was compared with the sulphurised sorbent. Investigation of the dynamic behaviour of adsorption fixed bed system which is highly demanded prior to industrialisation, was studied in the present work to predict the mass transfer coefficients and diffusional properties of adsorbent-adsorbate system. Therefore, a diffusional model namely Axial-dispersion Film Pore-Surface Diffusion model including all the main mass transfer mechanisms in porous beds was implemented. Apart from the mathematical model, one of the most common shortcut approaches (Thomas model) was applied to describe the adsorption behaviour in fixed beds for comparison with the mathematical model results. Based on the Thomas model and experimental results, several important properties of both adsorbate/adsorbent system such as equilibrium adsorption capacity and exhaustion rate were calculated and explained. According to the results of mathematical modelling, the factors and mechanisms with the lowest degree of importance were determined in each system, and the more appropriate/simpler mathematical models were suggested. [ABSTRACT FROM AUTHOR]

The current study deals with the removal of mercury ions from aqueous solutions by sulfurized and original activated carbons (ACs) in the batch and fixed bed modes. The modified sample containing sulfur groups showed higher uptake capacities and larger breakpoints. The XPS and EDS analyses confirmed the introduction of carbon–sulfur bonds onto the AC's surface after impregnation with dimethyl-disulfide. In the work, the diffusional models named, "Film Pore Concentration-Dependent Surface Diffusion (FPCDSD)" and "Axial dispersion Film Pore Concentration-Dependent Surface Diffusion (AFPCDSD)" were respectively applied to explain the batch and bed-mode kinetic data to clarify the rate-controlling mechanisms and estimate the diffusional/mass transfer properties of adsorbate–adsorbent systems. In all cases, the sulfurized AC showed greater Ds (surface diffusivity) values attributed to the higher mercury loading on this sorbent which facilitates ion hopping on the surface sites. The internal and film diffusions both played notable roles in mercury adsorption mechanism. [ABSTRACT FROM AUTHOR]

Pillared clays are special kinds of modified clays with significant and permanent porosity, produced by embedding columns or pillars between the layers of clay. However, these materials are very well-known for their catalytic properties; their adsorptive characteristics in wastewaters towards different classic and growing contaminants need to be studied comprehensively. The present work is performed to introduce different methods for clays' pillaring, the main steps of the process, comparison of various pillaring agents, etc. During recent years, several investigations have been carried out to find a way for pillared clays' modification (by introducing active chemical functional groups, doping, heat treatment, etc.) to achieve selective adsorbents towards specific pollutants. Therefore, the main modification techniques including surfactant modification, metal doping, etc. are introduced and classified in the present work. Furthermore, adsorptive applications of (modified) pillared clays towards organic, pharmaceutical, and metal ions pollutants, the relationship between physicochemical properties and adsorption performance of pillared clays, adsorption mechanisms, and quantitative comparison of pillared clays' ability for pollutants removal are the other issues that have been considered in the present work. [ABSTRACT FROM AUTHOR]