DOI: 10.14457/tu.the.2020.89
title: Characteristics and catalytic activity of activated carbon supported hydrotalcite for fermentative hydrogen production

description: Commercial activated carbon (CAC) was modified by a chemical activation agent, H3PO4 with the temperature ranging from 400 to 900°C (400°C, 500°C, 600°C, 700°C, 800°C and 900°C) for 1 h under N2 atmosphere. The modified commercial activated carbon (mCAC) samples were characterized for surface area, morphology, structure and functional groups to understand the roles of the modified activated carbon in fermentation. All samples (CAC and mCAC) were employed at a concentration of 8.33 g/L. The possible enhancement of hydrogen production via dark fermentation was investigated using sucrose as the substrate. The best catalytic performance was observed at an activation temperature of 600°C (mCAC600) with hydrogen production of 2.62 mol H2/mol sucrose. This was 17% higher than the control. The temperatures continuous to increase, great weight loss was produced at very high temperature practically 700 to 900°C by volatilization of phosphorous compound functional groups. Similar with the low temperature (400-500°C) caused change the characteristics of activated carbon as such a loss of weight, surface area and porosity reduction. In addition, the increment of hydrogen production was associated with the properties of activated carbon such as surface area, pore structure, and adsorption ability especially pore size. The mCAC600 has the biggest pore size (2.31 nm) compared to all treatments, which could improve microbial colonization and thereby, enhance the hydrogen production. The mCACs (400 to 700°C) were then used as a supporting material for Zn-Ni-HT. The Zn-Ni-HT/mCAC600 was obtained by the incipient impregnation method. The maximum hydrogen production yield was found at 2.95 mol H2/mol sucrose, which was 30% higher than the control. The possible reason is that mCAC600 has the biggest in pore size. When Zn-Ni-HT loaded on mCAC600, it could help HT spread in the pore. Therefore, Zn-Ni-HT/mCAC600 showed a good performance as compared to all materials. Moreover, both acetic and butyric acids were observed as by-product. The highest concentration of acetic acid was observed for Zn-Ni-HT/mCAC600, which also provided the highest hydrogen production yield. Zn-Ni-HT/mCAC600 had highest percent adsorption of VFAs particularly butyric acid, which was 63.78%. While the percent adsorption of VFAs for mCAC600 was found for butyric acid only 25.93%. Zn-Ni-HT/mCAC600 is 40% higher than mCAC600. Base on the Langmuir and Freundlich isotherm models, it shows that the volatile fatty acids were covered only by a monolayer on the surface of the materials. There is no stacking adsorbed molecules. Therefore, volatile fatty acids were adsorbed on the pore of the supported materials. It should be noted that Zn-Ni-HT/mCAC600 could be used once as gradual decline in performance was found for recyclability tests. The Zn-Ni-HT/mCAC600 acted as an alkaline reagent to encounter fatty acid, thereby preventing a pH drop during the fermentation process. Moreover, the supported activated carbon can also adsorb unfavorable VFAs in the system. The release of metal ions from the structure of Zn-Ni-HT/mCAC600 was lower than that of Zn-Ni-HT/CAC, especially for Mg2+ and Al3+. The released ions also helped to enhance the hydrogen production yield, particularly for Ni2+. It is, therefore, concluded the Zn-Ni-HT/mCAC600 composite created hybrid functions to promote fermentative hydrogen production.