Fixed-bed column adsorption studies of methylene blue dye from an aqueous  solution using silicon nitride adsorbent synthesized from sand and coffee husk  wastes

Ndung’u Samuel Ng’ang’a, Nthiga Esther Wanja, Wanjau Ruth Nduta, Gichumbi Joel  Mwangi

Fixed-bed column adsorption studies of methylene blue dye from an aqueous solution using silicon nitride adsorbent synthesized from sand and coffee husk wastes

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Date

2024

Authors

Ndung’u Samuel Ng’ang’a, Nthiga Esther Wanja, Wanjau Ruth Nduta, Gichumbi Joel Mwangi

Publisher

Sami Publishing Company (SPC)

Abstract

To address the challenge of increased demand for clean water globally, there is a need to treat the available wastewater. Textile dyes are carcinogenic and their discharge to the environment has been reported to degrade the esthetic properties of water bodies. It is imperative to assess textile dye levels in wastewater as well as decontamination to ascertain its safety. Conventional purification processes suffer from limitations in terms of efficiency, cost effectiveness and environmental effect. Attention has recently shifted to adsorption as an economical technique for textile dyes removal using low-cost adsorbents. The current study utilizes Silicon Nitride (Si3N4) as a novel adsorbent in evaluating its adsorptive ability for Methylene blue dyes from an aqueous solution. The adsorbent was prepared using extracted silica from sand and coffee husk biochar in an ammonia environment. The sand, extracted silica, raw and biochar samples and silicon nitride composites were characterized using X-Ray Fluorescence (XRF), Fourier Transform Infrared (FT IR), X-Ray Diffractometer (XRD), Scanning Electron Microscope (SEM), Energy Dispersive X Ray (EDX) and Thermogravimetric Analyzer (TGA). The results showed that the raw sand contain quartz, calcite, microcline and clinochlore. The results for the extracted silica showed a highly amorphous silica containing hydroxyl (-OH) and siloxane (Si-O-Si) functional groups. The alkali fusion process increased the silica content to > 92 % from 83 % with oxide impurities reduced to < 1 %. The characterization of biochar samples showed a highly amorphous, porous carbon structure with aromatic carbon bonds (C=C) and a negligible ash content. The characterization of Si3N4 powder showed thermally stable, porous and highly amorphous material with α-Si3N4 and β- Si3N4 phases. The FT-IR results functional groups of silicon-nitrogen (Si-N), silanol (Si-OH) and silicon-nitrogen-silicon (Si-N-Si) which were hydroxylated in an aqueous media to give silazane (Si2=NH2+) and silanolate (Si-O-) adsorbent sites for methylene blue (MB) dyes removal. A column capacity (47.01 mg/g) was reported at optimal values of 4 mL/min, 7 cm and 50 mg/L. Column dynamic modeling analysis revealed that Thomas and Yoon-Nelson models best fitted the breakthrough curves than Adam-Bohart model. The column performance using spiked water samples Athi showed that Si3N4 adsorbent had a lower efficacy than in a model solution with the maximum column adsorption capacity of 38.92 ± 0.04 mg/g. The results revealed the potential of Si3N4 adsorbent for decontamination of MB dyes from wastewater.