Abstract
The objective of this study was to study the structure and physicochemical properties of biochar derived from apple tree branches (ATBs), whose valorization is crucial for the sustainable development of the apple industry. ATBs were collected from apple orchards located on the Weibei upland of the Loess Plateau and pyrolyzed at 300, 400, 500 and 600 °C (BC300, BC400, BC500 and BC600), respectively. Different analytical techniques were used for the characterization of the different biochars. In particular, proximate and element analyses were performed. Furthermore, the morphological, and textural properties were investigated using scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, Boehm titration and nitrogen manometry. In addition, the thermal stability of biochars was also studied by thermogravimetric analysis. The results indicated that the increasing temperature increased the content of fixed carbon (C), the C content and inorganic minerals (K, P, Fe, Zn, Ca, Mg), while the yield, the content of volatile matter (VM), O and H, cation exchange capacity, and the ratios of O/C and H/C decreased. Comparison between the different samples show that highest pH and ash content were observed in BC500. The number of acidic functional groups decreased as a function of pyrolysis temperature, especially for the carboxylic functional groups. In contrast, a reverse trend was found for the basic functional groups. At a higher temperature, the brunauer–emmett–teller (BET) surface area and pore volume are higher mostly due to the increase of the micropore surface area and micropore volume. In addition, the thermal stability of biochars also increased with the increasing temperature. Hence, pyrolysis temperature has a strong effect on biochar properties, and therefore biochars can be produced by changing pyrolysis temperature in order to better meet their applications.
Highlights
Biochar is a carbon (C)-rich byproduct produced in an oxygen-limited environment [1], which has been gaining increasing attention over the last decade due to its potential to mitigate global climate change [2,3]
When the pyrolysis temperature increased from 300 to 500 ◦ C, the biochar yield sharply decreased from 47.94% to 31.71%
While, when the pyrolysis temperature further increased from 500 to 600 ◦ C, the biochar yield only decreased from 31.71% to 28.48%
Summary
Biochar is a carbon (C)-rich byproduct produced in an oxygen-limited environment [1], which has been gaining increasing attention over the last decade due to its potential to mitigate global climate change [2,3]. Biochar can be used as a soil amendment with the aim of improving soil physical, chemical and biological properties [4,5], and as an adsorbent to remove organic and inorganic pollutants [6,7]. Various types of biomass (wood materials, agricultural residues, dairy manure, sewage sludge, et al.) have been used to produce biochars under different pyrolysis conditions [9,10]. Biomass undergoes a variety of physical, chemical and molecular changes [11]. Previous studies indicated that pyrolysis condition and feedstock type significantly affect the structural The functions and applications of biochars mostly depend on their structural and physicochemical properties [8], it is very important to characterize the structural and physicochemical properties of biochar before its use.
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