Contamination of water with organic dyes is a major environmental concern as it causes serious life-threatening environmental problems. The present research was designed to evaluate the potential of three different natural inorganic clays (NICs) i.e., Pakistani bentonite clay (PB), bentonite purchased from Alfa Aesar (BT), and Turkish red mud (RM) for malachite green (MG) dye removal from an aqueous solution. Various analytical techniques, namely X-ray fluorescence spectrometry (XRF), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), Brunauer–Emmett–Teller surface area measurement (BET), and thermogravimetric analysis (TGA), were used to investigate the physicochemical properties of the NICs samples. The effect of adsorption operational parameters such as contact time, aqueous phase pH, dye concentration, and amount of NICs on the adsorption behavior of MG onto NICs samples were investigated under the batch adsorption system. The equilibrium and kinetic inspection reflected the best description of MG adsorption behavior by the Langmuir isotherm model and pseudo-first-order kinetic model, respectively. The results indicated that the adsorption was favorable at higher pH. The maximum adsorption capacities calculated by Langmuir isotherm for PB, BT, and RM were found to be 243.90 mg/g, 188.68 mg/g, and 172.41 mg/g, respectively. It can be concluded that natural inorganic clays with a higher surface area can be used as an effective adsorbent material to remove the MG dye from an aqueous solution.

In this work, highly crystalline CdS nanorods (NRs) were successfully synthesized by a facile, one-step solvothermal method. The as-prepared CdS NRs powder was characterized by XRD, FESEM, Raman, PL, XPS, BET, and UV-visible techniques to evaluate the structural, morphological, and optical properties. The photocatalytic performance of the as-synthesized CdS NRs was investigated for the photodegradation of RhB dye under visible light irradiations. It has been found that CdS NRs show maximum RhB degradation efficiency of 88.4% in 120 min. The excellent photodegradation ability of the CdS NRs can be attributed to their rod-like structure together with their large surface area and surface state. The kinetic study indicated that the photodegradation process was best described by the pseudo-first-order kinetic model. The possible mechanism for the photodegradation of RhB dye over CdS NRs was proposed in this paper.

Adsorption kinetics of malachite green and methylene blue from aqueous solutions using surfactant-modified organoclays

Clay minerals can effectively adsorb contaminants from aqueous effluents due to their good adsorption and high cation exchange capacity. However, naturally occurring clay materials possessing hydrophilic features are not especially effective for the removal of organic pollutants. Therefore, in the present work the issue of hydrophilicity is tackled by modification of the clay (Pakistan origin) to prepare organoclays. Hexadecylpyridinium chloride, cetyltrimethylammonium bromide, and sodium dodecyl sulfate were used as clay modifiers. Changes in the basal spacing of clay layers after modification with surfactants were determined through XRD analysis. Chemical compositions of the clay and organoclays were determined by FTIR spectroscopy. Surface morphology of the as-prepared organoclays was assessed from SEM analysis. The modified clays (organoclays) were tested for their ability as potential adsorbents for three dyes from water: brilliant green, ethyl violet and allura red. All three modified clays showed high adsorption characteristics by removing (>90 %) of all three dyes with an adsorption capacity ranging from 35 to 85 mg/g. The time-dependent adsorption experiments showed that the rates of adsorption of dyes on organoclays were fast, adsorbing maximum amounts of dyes ranging from 15 to 80 mins of contact time. The adsorption kinetic study revealed that the dye removal process is mainly governed by a pseudo-1st order mechanism. Thus, surfactant-modified clays are an excellent choice as cost-effective and efficient adsorbents for the purification of water from dye contaminants.