Enhanced Cr(VI) adsorption using chemically modified dormant Aspergillus niger spores: Process and mechanisms

Adsorption materials based on Aspergillus niger spores were synthesized with chemically modified surfaces, and the CTAB surface modification adsorbent was the best. Zeta potential was in the range of pH 1 to pH 4.38, and CTAB-modified spores (CMS) surface had a positive charge, leading to adsorption of negatively charged chromic acid ions. The biosorption capacity of CMS was also markedly increased. The maximum biosorption capacity reached 177 mg/g following CTAB modification. XPS and FTIR confirmed the importance of secondary amine in the reduction adsorption process. Secondary amine (-NH-) transfer electrons to unoccupied orbit of the Cr(VI) for the reduction of hexavalent chromium. At the same time, chromium(III) is coordinated with OC-O functional group and (NH+/N+) and adsorbed on the modified spores. The fungal biological adsorbent can adsorb and desorb hexavalent chromium for five consecutive times without a clear decrease.