Effects of transition metal-involvement on thermal behavior of mushroom residue and physicochemical properties and adsorption performance for methyl orange of corresponding biochars

Abstract: Mushroom Residue (MR) is one of the most abundant edible fungus residues in China. In this study, an efficient and feasible way was proposed for the resource utilization of edible fungus residues. Transition metals were also employed to treat the MR. An investigation was made to clarify the effects of transition metal concentration (0-5mmol/g), transition metal anions (Cl-, NO3-, and SO42-), and transition metal types (Fe, Zn, and Mn) on the thermal behavior of MR. The surface functional groups, pH values, proximate and ultimate analysis were then utilized to evaluate the physicochemical properties of the biochars. The potential application as an adsorbent was treated to simulate the methyl orange-contaminated wastewater. Thermogravimetric analysis showed that the main pyrolysis zone of MR was 197.83-418.22℃, and the maximum weight loss rate occurred at 351.40 ℃ with the maximum weight loss rate of 7.61%/min. The transition metals greatly contributed to the main pyrolysis region of MR shifting to a lower temperature zone, where the temperature was reduced to the maximum weight loss rate. This was highly dependent on the type of transition metal anion, concentration, and type of transition metal. Particularly, the one pre-treated with 5 mmol/g FeCl3 (MR-FeCl3-5) showed a significant effect on the decrease of the pyrolysis zone among all samples. The main pyrolysis range of MR-FeCl3-5 was 130.93-335.00℃ and the maximum weight loss rate emerged at 201.63℃ with a maximum weight loss rate of 2.28%/min. Similarly, the activation energy of MR was 34.04kJ/mol. There was also a great reduction with the introduction of transition metals. Among them, the MR-FeCl3-5 presented the lowest activation energy of 5.41 kJ/mol. The FT-IR results reveal that the biochar prepared from the MR without the transition metal treatment under 400 ℃ (MR-FeCl3-0-400C) shared the abundant surface functional groups, such as -OH, C-H, C=O, C-O, and C=C. The introduction of transition metals generally resulted in the decrease of oxygen-containing functional groups (C-O, and C=O) and the enhancement of C=C functional groups in the biochars. Ash content, fixed carbon, and volatile matter of MR-FeCl3-0-400C were 17.91%, 35.85%, and 44.44%, respectively, under the proximate analysis. The transition metals caused an increase in the ash content and fixed carbon, where there was a decreasing trend of volatile matter for the biochars. Therefore, the presence of transition metals effectively promoted the degradation of the organic composition in the MR (hemicellulose, cellulose, and lignin). Moreover, there was a decrease in the C and H of the biochars derived from transition metal-treated MR after ultimate analysis, compared with MR-FeCl3-0-400C. The pH value of MR-FeCl3-0-400C was 8.68, which was attributable to the high content of intrinsic ash in the MR. A severe decrease of the biochars was achieved in the treatment of FeCl3 and Fe2(SO4)3. By contrast, the biochar treated by Fe(NO3)3 showed a pH value close to the MR-FeCl3-0-400C. A superior adsorption performance of MR-FeCl3-5-400C was obtained for the methyl orange, compared with the MR-FeCl3-0-400C and the rest of the biochars. The theoretical maximum adsorption capacity (35.21 mg/g) was calculated from the Langmiur adsorption isotherm model, which was comparable with most of the carbon-based adsorbents. Anyway, the transition metals can be expected to convert the edible fungus residues into high value-added carbon materials, such as biochar. The finding can be a feasible way for the resource utilization of edible fungus residues.