Graphene oxide edge grafting of polyaniline nanocomposite: an efficient adsorbent for methylene blue and methyl orange

Highly efficient, bioactive, and bifunctional sorbent p-n-p visible light heterogeneous photocatalyst utilizing ultra-fine ZnS nanoparticles embedded in a polymeric nanocomposite

This study reports the successful synthesis of a ZnS@GO@Pani polymeric nanocomposite (NC) via chemical polymerization. The product was used for simultaneous photocatalytic degradation-adsorption of malachite green (MG), a carcinogenic and widely used dye. The physicochemical properties of the prepared NC were characterized by various techniques. Morphological and XRD results confirmed the fine size of ZnS nanoparticles (NPs) with an approximate mean size of 5 nm, uniformly distributed within the polymeric matrix. For comparative purposes, photocatalytic dye degradation-adsorption of this nanohybrid was explored both in the dark and under natural light. It was observed that 0.1 g of the ternary NC in MG aqueous solution (20 ppm) leads to dye adsorption within 15 minutes with an efficiency of 70% under dark conditions. Also, MG removal efficiency of up to 90% was achieved in 15 minutes under natural light owing to integrated photocatalytic degradation-adsorption mechanisms. Adsorption isotherm studies were performed considering Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (D-R) models. The results showed that the Freundlich isotherm with R 2 = 0.988 is well consistent with the experimental data. Integrated photocatalytic degradation-adsorption kinetics were modeled with pseudo-first-order (PFO) and pseudo-second-order (PSO) models where PSO with R 2 = 0.999 best fitted the data, implying the predominant role of chemical adsorption in the dye removal process. Antibacterial tests revealed superior antibacterial activity of the prepared ZnS@GO@Pani NC against both Gram-negative and Gram-positive bacteria, demonstrating the remarkable synergistic effect of ZnS NPs embedded in the GO@Pani matrix. Accordingly, the prepared NC could be regarded as a promising candidate for wastewater treatment applications. The leaching and regeneration studies also confirmed that the prepared NC is a non-toxic dye removal agent with good reusability.

Carbon Based Polymeric Nanocomposites for Dye Adsorption: Synthesis, Characterization, and Application

Agglomeration and restacking can reduce graphene oxide (GO) activity in a wide range of applications. Herein, GO was synthesized by a modified Hummer's method. To minimize restacking and agglomeration, in situ chemical oxidation polymerization was carried out to embed polyaniline (PANI) chains at the edges of GO sheets, to obtain GO-PANI nanocomposite. The GO-PANI was tested for the adsorptive removal of brilliant green (BG) from an aqueous solution through batch mode studies. Infrared (FT-IR) analysis revealed the dominance of hydroxyl and carboxylic functionalities over the GO-PANI surface. Solution pH-dependent BG uptake was observed, with maximum adsorption at pH 7, and attaining equilibrium in 30 min. The adsorption of BG onto GO-PANI was fit to the Langmuir isotherm, and pseudo-second-order kinetic models, with a maximum monolayer adsorption capacity (q_m) of 142.8 mg/g. An endothermic adsorption process was observed. Mechanistically, π-π stacking interaction and electrostatic interaction played a critical role during BG adsorption on GO-PANI.

Study of the adsorption of an organic pollutant onto a microporous metal organic framework

In this study, the microporous metal organic framework-5 (MOF-5) has been synthesized to be used to remove methyl orange by adsorption. The adsorption experiments exhibit a good adsorption capacity at a catalyst dose of 0.1 g L^-1 and for an initial concentration of 200 mg L^-1, whereas the performance is stable over a wide pH range. The equilibrium adsorption data showed a sigmoidal course, which is well fitted by the Dubinin-Astakhov model applicable for physical adsorption processes (E = 0.055 kJ mol^-1) onto heterogeneous surfaces and a more homogeneous pore structure (n = 9.9), with a maximum adsorption capacity of 1248.35 mg g^-1. As can be observed from the evaluation of the kinetic data, the surface of the adsorbent is heterogeneous with different active sites for methyl orange (MO) adsorption. Moreover, based on the rate constant, it can be suggested that there is a specific interaction like electrostatic interaction between MO and the adsorbent for rapid and high uptake of the dye, whereas the adsorption phenomenon is reversible. According to the adsorption mechanisms, intra-particle and film diffusion models simultaneously controlled the rate sorption, which was confirmed by the calculated intra-particle diffusion and the film diffusion coefficients. The evaluation of the thermodynamic parameters revealed that the MO adsorption is spontaneous, endothermic and the randomness increases with the adsorption of MO.

Two-step modification towards enhancing the adsorption capacity of fly ash for both inorganic Cu(II) and organic methylene blue from aqueous solution

A new adsorption material from fly ash (FA) was prepared by a two-step surface modification process, which showed higher ability for the removal of both inorganic and organic cationic pollutants from aqueous solution, i.e., Cu²⁺ and methylene blue (MB). Firstly, FA was modified by hydrothermal method in alkaline solution at 80 °C (FA80) to have a larger BET surface area. Afterwards, FA80 was further modified by sodium dodecyl benzene sulfonate (SDBS), of which a layer of anionic functional groups were grafted on the surface. The adsorption performance of SDBS@FA80 for removal of Cu²⁺ and MB were detailedly investigated. The results showed that SDBS@FA80 presented the optimal adsorption capacity at pH 7.0. Additionally, the maximum adsorption capacities of SDBS@FA80 for the removal Cu²⁺ and MB were up to 227.3 and 50.76 mg g^-1 at 70 °C, respectively, as well as being about three times higher than that of FA. When the initial concentrations of Cu²⁺ and MB were lower than those of 20 and 10 ppm, their removal efficiencies were as high as 99.75 and 96.4%, respectively. The pseudo-second-order model was well applied to describe the adsorption kinetics, indicating that chemisorption was taking place. Furthermore, a plausible mechanism is proposed by XPS studies, where the high adsorption capacity is mainly contributed to the electrostatic attraction and π-π stacking interaction between the cationic Cu²⁺/MB and anionic functional groups of SDBS. Due to the low-cost and high adsorption capacity, SDBS@FA80 is regarded as a promising adsorbent for the removal of cationic pollutants.