Hybrid Carbon Nanochromium Composites Prepared from Chrome-Tanned Leather Shavings for Dye Adsorption
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Every year, the leather tanning industry produces substantial quantities of residues such as chrome-tanned leather shavings (CTLS), which contain considerable amounts of Cr(III) salts. The residues have no particular value and under natural conditions can transform into toxic Cr(VI) wastes. The objective of the present work is to evaluate the transformation of these residues into carbon adsorbents at low temperatures (< 600 °C), using ZnCl2 as an activating agent. The pyrolysis temperature and residence times were studied. The materials were characterized and qualified by Acid Black 210 (AB) adsorption. The results indicated that low amounts of chromium oxides (less than 2% of Cr), in the form of 50–200 nm particles, remained after the synthesis procedure. The deposited chromium oxides were present in (II), (III), and (IV) oxidation states. The low preparation temperatures employed prevented further chromium oxidation to Cr(VI). Maximum surface areas of 439 m2/g were obtained. The materials efficiently removed AB (maximum experimental adsorption capacity of 44.4 mg/g) by means of electrostatic interaction caused by the positively charged distribution of the carbons. The adsorption capacity was not affected by temperature, but pH had a mixed effect due to the combination of a shift in surface charge distribution and dye speciation. The results demonstrated that it is possible to obtain a value-added product, i.e., carbons modified with chromium nanoparticles for dye removal, from a hazardous residue of the tanning industry.
KeywordsTannery Chrome-tanned leather shavings Activated carbon Adsorption Dye Acid Black 210 Chromium oxides
Technical assistance from Catalina De la Rosa and Ernesto Ornelas of CIATEC is acknowledged. The authors recognize support from LINAN and LANBAMA National Laboratories at IPICYT, as well as from Ana Iris Maldonado and Dulce Partida for the microscopy analysis and surface area measurements, respectively. FCB acknowledges SIP-IPN for financial support through the 20194931 project. Engineer Sebastian Pacheco at CICATA Altamira is acknowledged for XRD acquisition. XPS analysis was performed by Engineer Wilian Javier Cauich at the National Laboratory of Nano and Biomaterials at CINVESTAV-Merida, sponsored by the following projects: FOMIX-Yucatan, 2008-1081160 and CONACYT LA-2009-01-123913, 292692, 294643, 188345, and 204822.
This work was funded by the CIATEC A.C. (0FIA01602) and by the Ministry for Innovation of Guanajuato (Secretaria de Innovación del Estado de Guanajuato, SICES) through the SICES/058/2018 grant.
Compliance with Ethical Standards
The authors declare that they have no conflict of interest.
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