Effect of returning biochar from different pyrolysis temperatures and atmospheres on the growth of leaf-used lettuce.

The aim of this study is to evaluate the effects of biochar on the plant's growth. A pot experiment was carried out in our study. Rice straw-derived biochar were charred at two heating temperatures (400 °C/800 °C) and two oxygen-limited atmospheres (CO2/N2), respectively. The FESEM/EDS technique (field emission scanning electron microscopy with X-ray energy-dispersive spectroscopy) was used to study soils, biochar and plant samples. FESEM images indicated that the structure of the biochar was highly heterogeneous with larger macropores, which can enhance soil porosity. Fine soil mineral particles blocked the biochar inner pores and channels after returning biochar to soil. EDS analysis indicated that the Al and Fe contents increased on the surface of biochar after their returning, which reduced the toxicity of Al and Fe in the soil. The returning straw directly inhibited the growth of leaf-used lettuce. Four returning biochar all significantly improved leaf-used lettuce growth, and the effects of biochar prepared under 400 °C and a CO2 atmosphere were better than those prepared under 800 °C and a N2 atmosphere. Changes of nitrogen content in the biochar before and after their returning were consistent with the improvement of soil available nitrogen, and plant growth was positively correlated with the nitrogen content of biochar. This study explored the impact of biochar on soil nutrients and revealed the mechanism of biochar returning to the field to promote plant growth. It is of great significance in studying and improving the characteristics of soil nutrients.

Preparation of high porosity biochar materials by template method: a review.

Biochar plays an important role in soil improvement, pollutant removal, and nitrogen reduction. The excellent adsorption performance of biochar is closely related to its pore structure. Therefore, this paper combines a large amount of literatures to investigate the principle and method of preparing carbon materials by using the template method, and the idea of preparing high porosity biochar by template method was proposed. The results show that: (1) The specific surface area of the carbon materials prepared by the template method is more than 400 m2 g-1, and the total pore volume is more than 0.3 cm3 g-1, which is much higher than the biochar materials prepared under the traditional high temperature anoxic pyrolysis. (2) Compared with the hard template method, a soft template method with simple operation, low toxicity of the compound, and low cost is selected. (3) The lignin, which is also a hydrophilic carbon source similar to phenolic resin, can be used as an ideal carbon precursor. (4) In the selection of templating agents, the specific surface area and total pore volume of carbon materials prepared by using F127 as a template are relatively large, showing more excellent pore size performance. (5) Finally, the idea of using template method to prepare high porosity biochar is proposed: lignin extracted from straw material is used as precursor, block polymer F127 is used as template, an appropriate amount of a cross-linking agent and a solvent is added, and finally the target biochar material is prepared by pyrolysis carbonization.