Novel mesoporous nanocomposite of WS2/ZIF-9 for efficient adsorption of textile dyes from wastewater

Abstract

In this work, novel mesoporous nanocomposite of tungsten disulphide (WS2) and zeolite imidazole framework-9 (ZIF-9) has been successfully synthesized for the adsorption of carcinogenic textile dyes. Various characterization techniques revealed that the modification of WS2 nanosheets with ZIF-9, improved surface chemistry, textural properties, morphological features, surface area, and surface charge of synthesized nanocomposite. Field-Emission Scanning Electron Microscopy (FESEM) and High-Resolution Transmission Electron Microscopy (HRTEM) were used for the morphological details and analysis of size of polyhedrons with diameter of (∼1030 nm), length of each side of polyhedron (∼580 nm) and area of polyhedron ∼ 750 µm2, uniformly distributed on the surface of WS2 nanosheets. The enhanced specific surface area (∼114 m2/g) and micropores of as-synthesized nanocomposite as compared to pristine samples were confirmed by using Brunauer-Emmett-Teller (BET) analysis. A comparative adsorption study was performed using cationic and anionic dyes for determining the adsorption efficiency of pristine WS2 and ZIF-9 (WZF) nanocomposite. The adsorption capacity of as-synthesized materials was studied as a function of concentrations (2, 3 and 5 mg) for Malachite Green (MG) and Crystal violet (CV), textile dyes. The obtained higher adsorption capacity of WZF nanocomposite for CV (∼2124 mg/g) than MG (∼911 mg/g) is due to more electrostatic interactions between CV molecules and adsorbent because of having higher nitrogen groups in CV as compared to MG. The attained higher adsorption efficiency for MG and CV using synthesized WZF nanocomposite as compared to the pristine WS2 was explained on the basis of optimized surface charge (zeta potential study), large specific surface area (BET analysis) and lower recombination rate (TRPL study). The point of zero charge (PZC) was also analyzed by zeta potential studies at diversified values of pH for understanding the adsorption mechanism. The Langmuir isotherm provides best fit for the adsorption process with high value of R2: 0.99 and 0.97 (∼1) for both MG and CV dyes, respectively. The efficiency achieved throughout the four cycles of reusability study confirms the stability and regeneration ability of materials. Such novel nanocomposite has not been previously reported and opens the new pathways to highly efficient, affordable and highly mesoporous material for wastewater treatment.