Global concern on dyes-laden effluent has intensified over the years. Dyes are toxic, stable to light, and hardly oxidized and bio-degraded, hence causing severe physiological effects to living organisms. In water, dye hinders the light penetration for photosynthetic activity, consequently oxygen is deficient for respiration by aquatic creatures. Adsorption has been widely recognized as the effective removal strategy to abate dye wastewater. However, the quests to improve the adsorption efficiency are continuously sought through new adsorbents with special characters, while performing the removal process at optimum operating conditions. This short review aims to summarize the recent progress in adsorption studies of two commonly used industrial dyes, namely malachite green and congo red by various adsorbents. From the quoted studies, the oxidized mesoporous carbon yields a higher adsorption capacity of malachite green at 1265 mg/g, while Fe3O4@nSiO2@mSiO2 displays a greater capacity for congo red removal at 1429 mg/g. A superior adsorption relies not only on specific surface area but also the synergistic interactions of pore width and mesoporosity, surface chemistry, and operating conditions. The dyes properties and factors affecting the adsorption are also highlighted and discussed, with recommendations and future outlook.

No abstract

The present work was aimed at evaluating the adsorption properties of malachite green and congo red dyes by polyacrylonitrile carbon fibre sorbents. The sorbents were activated and oxidized using potassium hydroxide and ammonium persulfate, respectively at mild conditions. Consequently, the sorbents were characterized for surface area, surface functional groups and thermal decomposition. The activated sorbent displayed a 18.8 mg/g (94 %) of malachite green removal at Co = 20 mg/L, while both modified sorbents showed a 17.5 mg/g (87.5 %) removal of congo red at the same concentration. All sorbents showed a rapid equilibrium of malachite green and congo red dyes in water. Also, the sorbents are somewhat tolerable against different solution pH conditions despite a slight change due to possible electrostatic interactions. Thus, the materials could be successfully employed to treat dyes-laden wastewater.