Surface Functional Groups Of Biochar Research Articles

The biosorption capacity of biochar for 4-bromodiphengl ether: study of its kinetics, mechanism, and use as a carrier for immobilized bacteria.

Polybrominated diphenyl ethers (PBDEs) are known as ubiquitous pollutants in ecological systems and thus pose a great threat to the health of humans and other organisms due to their bioamplification and bioaccumulation along the food chain. The present study was designed to investigate the biosorption capacity of biochar for the removal of 4-monobromodiphengl ether and its synergistic effect when used as a carrier to immobilize the 4-monobromodiphengl ether-degrading strain Sphingomonas sp. DZ3. The raw biochar material was prepared by pyrolyzing maize straw at 350 °C under oxygen-limited conditions. The maximum biosorption capacity of biochar for 4-bromodiphengl ether was determined to be 50.23 mg/L under an initial concentration of 800 mg/L at pH 7.0 and 40 °C. The data obtained from the biosorption studies were fitted successfully with the pseudo-first-order kinetic and Freundlich isotherm models. The Weber-Morris model analysis indicated that intraparticle diffusion was the limiting step in the biosorption of 4-bromodiphengl ether onto the biosorbent. The values of thermodynamic parameters △G0 were calculated as -24.61 kJ/mol (20 °C), -24.35 kJ/mol (30 °C), and -23.98 kJ/mol (40 °C), △S(0) was -8.45 kJ/mol/K, and △H(0) was 21.36 kJ/mol. The artificial neural network analysis indicated that the initial concentration appeared to be the most influential parameter on the biosorption processes. The removal rate of 4-bromodiphengl ether achieved using the biochar-microorganism system was increased by 63 and 83% compared with the rates obtained with biochar and the strain individually, respectively. The morphology of the biochar and immobilized strain was determined using a scanning electron microscope, and information of the surface functional groups of biochar was obtained through an infrared spectra study.

Biochar of corn stover: Microwave-assisted pyrolysis condition induced changes in surface functional groups and characteristics

Biochar was prepared by microwave-assisted pyrolysis of corn stover at atmospheric pressure and different reaction temperatures and time. A central composite experimental design was used in the optimization of volatiles (bio-oil and syngas), biochar production, and the amount of carbon surface functional groups. Various types of oxygenated functional groups on the biochar were quantified by means of titrimetric techniques using a modified Boehm's method. The range of surface carbonyl groups amount was from 0.27 to 1.70mmol/g carbon. The produced biochars were also characterized in terms of the elemental composition, BET surface area and chemical structure. The maximum surface area of the biochar was 45m2/g. The result indicates that the surface functional groups of biochar were significantly influenced by the pyrolysis temperature and residence time. An adequate prediction model was developed to describe the development of carbon surface functional groups. Modification and characterization of biochar surface functional groups is a new way to improve or extend their catalytic application in biomass conversion and bio-oil upgrading.

Adsorption behavior comparison of trivalent and hexavalent chromium on biochar derived from municipal sludge

In this work, static equilibrium experiments were conducted to distinguish the adsorption performance between the two valence states of chromium on biochar derived from municipal sludge. The removal capacity of Cr(VI) is lower than 7mg/g at the initial chromium concentration range of 50–200mg/L, whereas that of Cr(III) higher than 20mg/g. It indicates that Cr(III) is much easier to be stabilized than Cr(VI). No significant changes in the biochar surface functional groups are observed before and after the adsorption equilibrium, demonstrating the poor contribution of organic matter in chromium adsorption. The main mechanism of heavy metal adsorption by biochar involves (1) surface precipitation through pH increase caused by biochar buffer ability, and (2) exchange between cations in solution (Cd2+) and in biochar matrix (e.g. Ca2+ and Mg2+). The reduction of Cr(VI) to Cr(III) is necessary to improve removal efficiency of chromium.

Influence of heating temperature and holding time on biochars derived from rubber wood sawdust via slow pyrolysis

Biochar samples were produced from rubber wood sawdust (RWSD), which is a by-product from sawmills, via slow pyrolysis. Biochar is a potential additive for agricultural soil as a soil amendment and for agronomics. The approach proposed in the current study considers the effects of heating temperature and holding time on the surface functional groups and morphologies of RWSD-derived biochars. The pyrolysis was performed in a vertical tube furnace heated at 5°C/min from room temperature to maximum heating temperatures of 300°C, 400°C, 500°C and 700°C under nitrogen gas purging at a rate of 30ml/min. Two sets of biochars were produced with holding times of (i) 1h and (ii) 3h. Proximate and ultimate analyses were performed on the raw RWSD using thermogravimetric analysis (TGA) and carbon–hydrogen–nitrogen (CHN) elemental analysis. The influence of heating temperature and holding time on biochar surface functional groups and porosities was investigated using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Boehm titration, pH alkalinity, Brunauer–Emmett–Teller (BET) surface area analysis, scanning electron microscopy (SEM) and SEM with energy-dispersive X-ray (SEM–EDX) spectrocopy. The FT-IR spectra indicated the presence of acidic functional groups, such as carboxylic, phenolic and lactonic groups, and these groups were quantified by Boehm titration. The number of acidic functional groups decreased as the heating temperature and holding time increased. The maximum amount of acidic functional groups was determined to be 1.9mmol/g at 300°C for a 1-h holding time compared to 1.3mmol/g for a 3-h holding time and 1.0mmol/g with a 1-h holding time at 700°C. All of the biochars produced at heating temperatures above 400°C were alkaline, and the pH value increased as the heating temperature and holding time increased. The biochar produced at 300°C with a 1-h holding time had a pH of 6.72 and the sample produced with a 3-h holding time had a pH of 7.67. In addition, the sample produced when the temperature was increased to 700°C with a 1-h holding time had a pH of 11.44. The BET surface area analysis reported maximum values of 5.49m2/g, and the total pore volume was 0.0097cm3/g at a heating temperature of 700°C with a 3-h holding time. SEM micrographs clearly showed the development of well-defined pores in the biochars, and the SEM–EDX spectra indicated localised carbon and oxygen content in all the samples. The results indicated that biochars produced from RWSD are potentially beneficial as soil amendments. However, an extensive study of biochar sustainability is worth investigating.

In situ and ex situ spectroscopic monitoring of biochar's surface functional groups

A number of studies concluded that peak pyrolysis temperature determines essential biochar properties: surface functional group, fixed carbon content, O/C, H/C, and BET surface area. Chemical (most importantly oxygen-containing surface functionalities), rather than physical (surface area) property of biochar dictates its ability to stabilize heavy metals in soil. Labile carbon fraction of biochar is rich in heavy metal coordinating functionalities, and recalcitrant carbon fraction is necessary for the long-term stability in soil. To produce desirable biochar properties with minimal time and cost, the slow pyrolysis platform must be optimized not only for the peak temperature, but additional parameters including the residence time and heating rate. In this study, time courses of biomass slow pyrolysis were investigated in the real time using a time-resolved (0.5s) in situ Diffuse Reflectance Infrared Fourier Transform (DRIFTs) to continuously monitor the changes in surface functionality. The greatest change in surface functionality was observed at 200–500°C from both in situ DRIFTs (during heating up at 10°Cmin−1 to reach the peak temperature) as well as ex situ (after a set residence time at the peak temperature) proximate, ultimate, attenuated total reflectance (ATR)-FTIR, and 1H NMR analyses of slow/fast pyrolysis and activated biochars. The FTIR spectral features at respective temperatures during in situ pyrolysis of lignocellulosic feedstock matched the peak temperature of post-production analysis. The FTIR peaks attributable to the oxygen-containing functional groups dramatically diminished after 20min residence time. Quantitative relationships were observed between parameters attributable to the aromatic characteristics: (1) baseline FTIR absorbance and (2) atomic H/C ratio with the fixed carbon content of biochar.

Influence of Pyrolysis Temperature on Biochar Property and Function as a Heavy Metal Sorbent in Soil

While a large-scale soil amendment of biochars continues to receive interest for enhancing crop yields and to remediate contaminated sites, systematic study is lacking in how biochar properties translate into purported functions such as heavy metal sequestration. In this study, cottonseed hulls were pyrolyzed at five temperatures (200, 350, 500, 650, and 800 °C) and characterized for the yield, moisture, ash, volatile matter, and fixed carbon contents, elemental composition (CHNSO), BET surface area, pH, pHpzc, and by ATR-FTIR. The characterization results were compared with the literature values for additional source materials: grass, wood, pine needle, and broiler litter-derived biochars with and without post-treatments. At respective pyrolysis temperatures, cottonseed hull chars had ash content in between grass and wood chars, and significantly lower BET surface area in comparison to other plant source materials considered. The N:C ratio reached a maximum between 300 and 400 °C for all biomass sources considered, while the following trend in N:C ratio was maintained at each pyrolysis temperature: wood≪cottonseed hull≈grass≈pine needle≪broiler litter. To examine how biochar properties translate into its function as a heavy metal (NiII, CuII, PbII, and CdII) sorbent, a soil amendment study was conducted for acidic sandy loam Norfolk soil previously shown to have low heavy metal retention capacity. The results suggest that the properties attributable to the surface functional groups of biochars (volatile matter and oxygen contents and pHpzc) control the heavy metal sequestration ability in Norfolk soil, and biochar selection for soil amendment must be made case-by-case based on the biochar characteristics, soil property, and the target function.