Biochar from vegetable wastes: agro-environmental characterization

Considering the global issue of vegetable wastes generation and its impact on the environment and resources, this study evaluated the conversion of four largely produced vegetable wastes (cauliflower, cabbage, banana peels and corn cob residues) into biochar. Each waste was tested individually and as a combined blend to assess feedstock influences on biochar properties. In addition, various pyrolysis temperatures ranging from 300 °C to 600 °C and two particle size fractions (less than 75 µm, 75–125 µm) were considered. Biochars were characterized for various properties that can influence the biochars’ effectiveness as a soil amendment. It was found that pyrolysis temperature was the most dominant factor on biochar properties, but that individual feedstocks produced biochars with different characteristics. The biochars had characteristics that varied as follows: pH 7.2–11.6, ECE 0.15–1.00 mS cm−1, CEC 17–cmolc kg−1 and ζ-potential − 0.24 to − 43 mV. Based on optimal values of these parameters from the literature, cauliflower and banana peels were determined to be the best feedstocks, though mixed vegetable waste also produced good characteristics. The optimum temperature for pyrolysis was around 400 °C, but differed slightly (300–500 °C) depending on the distinct feedstock. However, smaller particle size of biochar application was always optimal. Biochar yields were in the range of 20–30% at this temperature range, except for corn cobs which were higher. This study demonstrates that pyrolysis of dried vegetable wastes is a suitable waste valorization approach to produce biochar with good agricultural properties.Other Information Published in: Biochar License: https://creativecommons.org/licenses/by/4.0See article on publisher's website: http://dx.doi.org/10.1007/s42773-020-00069-9</p

XPS and material properties of raw and oxidized carbide-derived carbon and their application in antifreeze thermal fluids/nanofluids

In this study, the stability, thermal conductivity and viscosity of carbide-derived carbon antifreeze thermal fluids were explored. The study also compares the results between antifreeze suspensions prepared using oxidized CDC and emulsified CDC using gum arabic. At first, the raw CDC was oxidized with oxygen by acid treatment and the Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy results revealed an increase in the oxygen content and oxygen functional groups in oxidized CDC. The two-step method was utilized for CDC thermal fluids preparation. Sedimentation visualization and zeta potential testing were employed to investigate stability of nanofluids with time. The stability results revealed that the oxidized CDC has better stability and higher zeta potential values than the emulsified CDCs; however, both mixtures demonstrated stable suspensions for three months. Viscosity measurements showed that the gum arabic CDC suspensions have a higher viscosity than the oxidized CDC; the viscosity was growing with CDC and gum arabic loadings and decreased with temperature. The thermal conductivity analysis was carried out using a lambda analyzer in a temperature range of 288–338 K with a CDC mass loading range of 0.05–0.3 mass%. The experimental outcomes demonstrated that oxidized CDC suspension has better thermal conductivity than gum arabic emulsified CDC. The highest improvement in thermal conductivity was 25.6% using 0.3 mass% of oxidized CDC at 338 K. Moreover, raising the gum arabic mass loading was found to reduce the thermal conductivity enhancement. Therefore, according to the results, the oxidized CDC antifreeze suspensions can perform better than the emulsified CDC. Graphical abstractOther Information Published in: Journal of Thermal Analysis and Calorimetry License: https://creativecommons.org/licenses/by/4.0See article on publisher's website: http://dx.doi.org/10.1007/s10973-022-11419-z</p