Removal of methylene blue from water by NiO-modified silica gel

The objects of the study are sorption materials based on commercial silica gel and nickel (II) oxide with different mass ratios of NiO to SiO2: 1:1 and 0.5:1. To obtain such materials, expensive reagents and complex synthesis schemes are not required. In addition, they are distinguished by chemical stability, controlled morphology and have a significant number of reactive functional groups, which contributes to high adsorption capacity for various types of contaminants. The morphology of composite sorbents was studied using the electron microscopy method, the presence of a crystalline phase of nickel oxide on the amorphous surface of silica gel was investigated by X-ray phase analysis, and the successful application of a layer of nickel-containing compounds was confirmed by infrared spectroscopy. The main parameters of the mesoporous structure of the samples were determined by the method of low-temperature nitrogen adsorption/desorption. It was found that with an increase in the amount of the deposited oxide layer, the specific surface area and pore volume of the obtained sorbents decrease by 1.5–2 times compared to the original silica gel. The physicochemical features of the extraction of methylene blue dye by nickel-containing composites based on silica gel were studied. It was found that modification of the SiO2 surface with nickel (II) oxide leads to an increase in the sorption capacity of materials in relation to cationic dyes. It was shown that the highest sorption capacity is possessed by a sample with a mass ratio of NiO to SiO2 equal to 0.5:1. The maximum sorption value is 21 mg/g, which is almost 2 times higher than that for the original silica gel. The adsorption kinetics is adequately described by pseudo-first and pseudo-second order models, which indicates a high affinity of methylene blue with the surface of such samples. The results obtained indicate that the obtained sorption materials based on commercial silica gel and nickel (II) oxide can be used in the purification of water contaminated with organic cationic dyes.