Nanourchin ZnO@TiCN composites for Cr (VI) adsorption and thermochemical remediation. Issue 4 (August 2018)

• Record Type: Journal Article
• Authors: Rasaki, Sefiu Abolaji; Zhang, Bingxue; Liu, Siqi; Thomas, Tiju; Yang, Minghui
• Is Part Of: Journal of environmental chemical engineering. Volume 6:Issue 4(2018)
• Page Start: 3837
• Page End: 3848
• Publication Date: 2018-08
• Subjects: Titanium carbonitride -- Solid state separation -- Zinc oxide -- adsorption -- Cr (VI) gettering/separation; Chemical engineering -- Environmental aspects -- Periodicals; Environmental engineering -- Periodicals; Chemical engineering -- Environmental aspects; Environmental engineering; Periodicals; 660.0286
• DOI: 10.1016/j.jece.2018.05.040
• Languages: English
• ISSNs: 2213-2929

Abstract

Graphical abstract: Highlights: ZnO@TiCN nanourchin-composites are synthesized using solid–solid separation process followed by a wet deposition method. The system adsorbs Cr (VI) and thermochemically converts it to benign Cr (III). Entropy change and enthalpy associated with physisorption process is ∼18 kJ/mol.K and ∼5 kJ/mol. The adsorption process is pseudo-second order; high entropy correlates with the heterogeneity factor (∼3.9). Over 4 regeneration cycles, an adsorption capacity retention of >90% is observed. Abstract: ZnO@TiCN nanourchin composites are synthesized via a solid–solid separation process followed by a wet deposition method. The composite contains TiCN nanourchins, metallurgically connected to ZnO; the system adsorbs Cr(VI) following a pseudo-first order kinetics. This heterostructure has substantial ability to thermochemically convert the adsorbed Cr (VI) to Cr (III). Complete removal of Cr (VI) is achieved, even in the <10 ppm concentration regime. The effect of reaction time, temperature, pH value, adsorbent loading, initial concentration of Cr (VI), and thermodynamic parameters are systematically investigated. Van't Hoff's plot based analysis indicates that the entropy change associated with physisorption process involved is significantly positive (∼18 kJ/mol K). The process is also substantially endothermic (△H ∼ 5 kJ/mol). Kinetics improves with temperature up to 90 °C. The high entropy associated with the adsorption is attributed to a high heterogeneity factor of ∼3.9. Pseudo-second order is the best kinetic model to describe the adsorption of Cr(VI) onto the surface of ZnO@TiCN; both Freundlich and Langmuir isotherms describe the adsorption observed. Over 4 regeneration cycles, an adsorption capacity retention of >90% is observed. This novel adsorbent, with its hierarchical structure, and properties reported here, suggest that it could find applications in contemporary waste water treatment processes.