Physico-chemical characterization of biochars from vacuum pyrolysis of South African agricultural wastes for application as soil amendments

The physico-chemical properties of biochars from the vacuum pyrolysis of black wattle and vineyard annual prunings were investigated for their potential as soil amendments and compared to biochar from sugar cane bagasse. Biochar from sugar cane bagasse seems to be a promising sorbent and soil conditioner due to its high surface area, high surface acidity and microporous structure. This biochar can be applied to a wide pH range of soils for enhancing nutrient and water retention. On the other hand, the biochars from black wattle and vineyard possessing high concentrations of aromatic carbon, nutrients, and alkalinity are potential soil amendment agents. Black wattle biochar is more beneficial compared to biochar from vineyard due to its higher surface area, microporosity and cation exchange capacity. Therefore, this study recommends the utilization of biochars from black wattle as soil amendment agents especially in subtropical regions.     

Straw-based biochar mediated potassium availability and increased growth and yield of cotton (Gossypium hirsutum L.)

Potassium (K) being the major limiting factor affecting cotton yield and quality has received massive research attention and the effects of various K fertilization techniques/organic amendments have been studied extensively. However, it is not clear whether the straw based, high pH biochar affects K availability, lint yield and quality of the cotton crop in alkaline calcareous soils. In the present study, we carried out a field experiment on a moderate to strongly calcareous silt loam soil to demonstrate the effect of straw-based biochar and potassium application levels on the growth, seed cotton yield and the lint quality. The experimental treatments comprised of two factors, A) biochar types i) Control no biochar, ii) Rice husk biochar (RHB), iii) Wheat straw biochar (WSB), and iv) Rice straw biochar (RSB), factor B) potassium application levels (i) control, no K fertilizer application, ii) K at 15 kg ha⁻¹, and iii) K at 30 kg ha⁻¹ (4 × 3 × 3, n = 36). Results showed that overall cotton growth and yield was significantly improved with increasing rates of potassium application. Three biochar sources affected seed cotton yield and quality with varying effects. For instance, the RSB increased plant height (11.71% to 22.47%), number of bolls per plant (0.74% to 13.75%), average boll weight (35.44% to 36.22%), the seed cotton yield was increased by 14.48% over the control when rice straw biochar was applied in combination with potassium at 30 kg ha⁻¹. However, the ginning out turn (%) was declined with potassium application in combination with all three-biochar compared to control (no biochar addition). The WSB increased staple length and micronaire by 4.32% and 24.50% without potassium application. The potential effects of straw based biochar and potassium application on seed cotton yield and quality deserve further studies to identify the most suitable biochar as per soil chemical properties.     

Recent application of biochar on the catalytic biorefinery and environmental processes

Biochar, produced and activated from thermochemical methods, was applied as catalyst for catalytic biorefinery and environmental pollutant removal. In this review, recent advanced studies of biochar catalyst were discussed.     

129Xe NMR Studies of Pecan Shell-Based Biochar and Structure-Process Correlations

Pecan shell-based biochar is utilized as a filtration medium, sequestrant for metallic ions, soil conditioner, and other applications. One process for creating the biochar involves the use of phosphoric acid at high temperature in a partial oxygen atmosphere to produce a highly porous carbonaceous material. In this work, we found ¹²⁹Xe NMR to be an excellent technique to study micropores in biochar. Thus, the ¹²⁹Xe chemical shift in biochar was found to vary linearly with the xenon pressure; from the data an estimate of about 8–9 Å could be proposed for the average pore diameter in pecan shell-based biochar. Through saturation recovery and 2-D NMR exchange experiments, information on the exchange between free versus bound xenon was obtained. Furthermore, correlations of ¹²⁹Xe NMR data with the carbonization process conditions were made.     

Recent application of biochar on the catalytic biorefinery and environmental processes

Lignocellulosic biomass is an abundant and environment-friendly source for renewable energy production. The value and application of biochar, which is obtained from the thermochemical conversion of biomass, is increasing rapidly because of its high carbon content and porosity. The property of biochar, such as surface area, porosity, and number of functional groups, can be improved by controlling the conditions of biomass conversion, biochar activation, and functionalization methods. The production and activation of biochar as well as its potential use for soil remediation, pollutant adsorption, and biorefinery have been reviewed extensively over recent decades. This paper provides a conceptual approach for biochar production and activation together with its application as a catalyst for biorefineries and the removal of environmental contaminants.     

Iron-based biochar as efficient persulfate activation catalyst for emerging pollutants removal: A review

In recent years, biochar (BC) as a low-cost, easily available biomass product, is widely applied in sulfate radical-based advanced oxidation processes (SR-AOPs) for emerging pollutants remediation. Herein, a state-of-art review of iron-based biochar catalysts is currently available in SR-AOPs application. A general summary of the development of biochar and the catalytic properties of biochar is presented. Especially, the synthetic strategies of different types of iron-based biochar catalysts are discussed. Moreover, the theoretical calculation to interpret the interaction between biochar and iron species is discussed to explore the activation mechanisms. And the regeneration methods of biochar-based catalyst are presented. The unresolved challenges of the existent biochar-based SR-AOPs are pointed out, and the outlooks of future research directions are proposed.     

植物源生物炭材料的制备及其在农药残留领域中的应用进展北大核心CSCD

随着农药的广泛使用,其已普遍存在于环境中,对人们的身体健康产生巨大影响。因此,环境中农药残留的去除和分析检测对保护人体安全健康至关重要。同时,农药在环境中残留浓度低,需要一种对目标物有较强选择性和富集作用,并对环境影响小的前处理吸附剂。植物源生物炭是由植物源生物质作为碳源衍生得到的材料,其比表面积大、孔容量高、表面官能团可调节,且环境相容性好,其原料植物源生物质的价格低廉、来源广泛并可再生,是一种廉价高效的吸附剂。该文主要综述了近10年来植物源生物炭用于环境中农药残留去除和分析检测前处理的应用进展。其中在农药残留去除方面的应用主要包括降低农药在土壤中的移动性,修复手性农药造成的污染,负载降解农药的细菌及作为化肥的缓释载体。在农药残留分析检测前处理方面,植物源生物炭可用作分散固相萃取、固相微萃取和磁性固相萃取的吸附剂来选择性吸附水果和蔬菜中的有机磷类和三唑类农药,以及水环境中的有机氯类农药。另外,还介绍了植物源生物炭的吸附机理,详细阐述了基于计算模拟如密度泛函理论、分子动力学模拟和巨正则蒙特卡洛模拟的吸附机理研究并讨论了其优势。最后,总结了植物源生物炭在农药去除和农药残留分析检测前处理方面应用的优势,指出了其在农药残留领域应用待解决的问题。     

Characterization and Artificial Neural Networks Modelling of methylene blue adsorption of biochar derived from agricultural residues: Effect of biomass type,pyrolysis temperature,particle size

Biochar has been explored as a sorbent for contaminants, soil amendment and climate change mitigation tool through carbon sequestration. Through the optimization of the pyrolysis process, biochar can be designed with qualities to suit the intended uses. Biochar samples were prepared from four particle sizes (100–2000 µm) of three different feedstocks (oak acorn shells, jift and deseeded carob pods) at different pyrolysis temperatures (300–600 °C). The effect of these combinations on the properties of the produced biochar was studied. Biochar yield decreased with increasing pyrolysis temperature for all particle sizes of the three feedstocks. Ash content, fixed carbon, thermal stability, pH, electrical conductivity (EC), specific surface area (SSA) of biochar increased with increasing pyrolysis temperature. Volatile matter and pH value at the point of zero charge (pH_pzc) of biochar decreased with increasing pyrolysis temperature. Fourier-transform infrared spectroscopy (FTIR) analysis indicated that the surface of the biochar was rich with hydroxyl, phenolic, carbonyl and aliphatic groups. Methylene blue (MB) adsorption capacity was used as an indicator of the quality of the biochar. Artificial neural networks (ANN) model was developed to predict the quality of the biochar based on operational conditions of biochar production (parent biomass type, particle size, pyrolysis temperature). The model successfully predicted the MB adsorption capacity of the biochar. The model is a very useful tool to predict the performance of biochar for water treatment purposes or assessing the general quality of a design biochar for specific application.     

Pyrolysis of agricultural residues from rape and sunflowers: Production and characterization of bio-fuels and biochar soil management

This research explores the opportunities of combining energy production with a biochar soil management using a pyrolysis process. Real-world issues justify this approach: the need to provide sustainable production systems that minimize on- and off-site pollution and soil degradation; and the demand for solutions to global warming. The proposed technology is a pyrolysis process that yields gas, bio-oil and biochar. The composition and heating value of the gas makes it suitable for use as a fuel. The bio-oil obtained may be evaluated as an environmentally friendly green biofuel candidate. The biochar product is carbon-rich and a potential solid biofuel. Other ways it might be used as a C and N source in soil amendment. This is a key to securing environmental benefits: the production of a biochar which can be applied to soil.     

草酸改性空气凤梨生物炭吸附甲醛的机理研究

探究草酸改性园林废弃物类生物炭对溶液中甲醛的吸附效率和固定的机理,为园林废弃物类生物炭在甲醛污染控制方面的应用提供科学依据。利用马弗炉在低氧条件下将空气凤梨原材料和草酸改性后的原材料制备成生物炭。然后利用实验室模拟法,研究不同反应时间、甲醛浓度、pH对生物炭吸附效果的影响,并分析草酸改性如何提高园林废弃物类生物炭对甲醛的吸附性能。(1)生物炭对乙酰丙酮和酚试剂两种甲醛检测方法的精度有影响,对乙酰丙酮检测法的影响较小;(2)相比于未改性生物炭,草酸改性通过酸化分解杂质能够使改性生物炭比表面积提高约17倍,孔隙体积增加195.9%;(3)草酸改性后生物炭对甲醛的吸附量为11.6 mg g^-1,比未改性生物炭提高了12.95%,并且在60 min时趋于吸附平衡的状态;(4)Boehm滴定法表明草酸改性能够显著提高制备后生物炭上的官能团(羧基51.8%,羰基13.7%和内酯基35.9%),但酚羟基(4.5%)含量增加不明显,而相关性分析证实比表面积、羧基和内酯基官能团的增加是提高生物炭吸附甲醛的主要因素。实验证明,空气凤梨制备成生物炭用于溶液中甲醛的吸附是可行的,并且草酸改性能够进一步通过官能团提高其吸附能力,这为园林废物资源化利用提供了新的思路。     

生物质炭的制备、改性以及在挥发性有机物吸附方面的应用

挥发性有机物（VOCs）是大气中重要的污染源之一,对环境和人类健康产生严重的危害。吸附法是工业中最常用的去除VOCs的方法,吸附剂是吸附技术的关键,生物质炭是一种由生物质基材料在高温下热解活化等工艺制得的炭材料,具有较高的比表面积、丰富的孔隙结构和化学活性表面,在环境污染控制领域具有广泛应用。基于最近的研究,本文系统地综述了常用于去除VOCs的生物质炭的制备和改性方法,以及生物质炭在吸附VOCs的应用研究。本文首要目标是评估生物质炭去除VOCs的能力,特别是经过各种改性和活化工艺后,评价生物质炭作为吸附剂去除VOCs的适用性;确定改性和活化后对VOCs吸附能力的影响;揭示生物质炭对VOCs可能存在的吸附机理。最后,文章也对生物质炭的再生提出了建议和展望。     

Revolutions in algal biochar for different applications: State-of-the-art techniques and future scenarios

Algae are potential feedstock for the production of bioenergy and valuable chemicals. After the extraction of specific value-added products, algal residues can be further converted into biogas, biofuel, and biochar through various thermochemical treatments such as conventional pyrolysis, microwave pyrolysis, hydrothermal conversion, and torrefaction. The compositions and physicochemical characteristics of algal biochar that determine the subsequent applications are comprehensively discussed. Algal biochar carbonized at high-temperature showed remarkable performance for use as supercapacitors, CO₂ adsorbents, and persulfate activation, due to its graphitic carbon structure, high electron transport, and specific surface area. The algal biochar produced by pyrolysis at moderate-temperature exhibits high performance for adsorption of pollutants due to combination of miscellaneous functional groups and porous structures, whereas coal fuel can be obtained from algae via torrefaction by pyrolysis at relatively low-temperature. The aim of this review is to study the production of algal biochar in a cost-effective and environmental-friendly method and to reduce the environmental pollution associated with bioenergy generation, achieving zero emission energy production.     

Ball-milled synthesis of maize biochar-ZnO nanocomposite (MB-ZnO) and estimation of its photocatalytic ability against different organic and inorganic pollutants

Different industrial and agricultural practices release a variety of dyes and pesticides in soil and water. Degradation of these pollutants is very important to avoid health and environmental issues. In this study, the photocatalysis technique has been optimized and adopted to degrade organic and inorganic pollutants. First of all, biochar with distinctive physicochemical properties, like high specific surface, highly carbonaceous property, and the electron-conductive nature was prepared in a vacuum furnace from maize straw. These properties depicted the effective absorbance ability of prepared biochar. Using a solvent-free ball-milling method, ZnO loaded maize biochar nanocomposite (MB-ZnO) was synthesized from this biochar and used as a photocatalyst to degrade aqueous pollutants, under different light sources. The adsorption and photocatalytic activity of MB-ZnO was assessed against Safranin O (Saf) and Mancozeb (MC) within a closed system using different light conditions including dark, UV and visible light. To understand the mechanism of Saf and MC removal from aqueous solution, reaction kinetics was calculated according to the pseudo-first-order kinetic model. MB-ZnOcomposite exhibited variable photocatalytic performances to degrade Saf under visible light (83.5%), UV radiations (81.0%) and dark conditions (78%) in 60 min. Similarly, maximum MC degradation by MB-ZnO nanocomposite was exhibited in visible light (56.5%), followed by UV radiations (27.5 %) and dark conditions (25.2%). The findings of this study concluded that MB-ZnO nanocomposite can be used as an excellent catalyst to remove aqueous pollutants, under both light and dark conditions.     

Conversion of spent coffee grounds to biochar as promising TiO2 support for effective degradation of diclofenac in water

A novel composite, biochar derived from spent coffee grounds with immobilized TiO₂ (biochar–TiO₂) was prepared, characterized, and applied as an alternative, effective, and sustainable photocatalyst for degrading diclofenac from aqueous solution. Composites with different mass ratios between TiO₂ and biochar were prepared by mechanical mixing and subsequent pyrolysis in an inert atmosphere of N₂ at 650°C. The sample with biochar–TiO₂ ratio of 1:1 presented a degradation efficiency of 90% at just 120 min versus 40% for TiO₂ used as reference. This fact is associated with a set of intrinsic characteristics obtained during the formation of the composite, such as superior pore size, avoiding the recombination of the ē/h⁺ pair, bandgap reduction, and promotion of reactive oxygen species due to phenolic groups present on the biochar surface. The dominant reactive species involved during the photocatalytic degradation of diclofenac were h⁺ and ^•OH. The diclofenac degradation pathways were determined based on the identification of intermediates and nonpurgeable organic carbon (NPOC) analysis. The novel biochar–TiO₂ composite prepared in this work showed high physical–chemical stability and efficiency over five consecutive cycles of reuse, proving to be a highly promising photocatalyst for degrading diclofenac in water.     

Optimization of Oxygen Parameters for Determination of Carbon and Nitrogen in Biochar Materials

Recently, there has been increased focus on biochar materials due to their ability to sequester carbon for long-term in soil. In the production of biochar or charcoal, plant biomass is heated in a low or no oxygen environment. This process results in a product with unique characteristics. But there is limited research on the standardization of methods for determining total carbon (C) and nitrogen (N) in the biochar materials whose properties vary by feedstock type and pyrolytic conditions. The objective of this study was to determine the oxygen dosing time (OT) and dose (OD) for total organic carbon (TC) and nitrogen (TN) analysis in biochar materials by dry combustion method (using Vario Max CNS analyzer). Central composite rotatable design was used to determine the effect of five levels of oxygen dosing time (OT) and dosing level (OD) on measurement of total carbon and total nitrogen in four types of plant originated biochars. OT and OD level interaction had significant impact on the measurement of TC and TN in all types of biochar materials. Optimum levels of OT and OD were determined as 103 to 110 sec and 180 to 232 ml/min, respectively.     

Estimation of the molecular mass range of the tar from pyrolysis of casein by gas chromatography-mass spectrometry, probe mass spectrometry and size exclusion chromatography with 1-methyl-2-pyrrolidinone as eluent

Casein has been pyrolysed to obtain a biochar (28.3% yield), with mostly meso- and macro-pore structure, and a liquid tar product of high yield (37.5%) with the balance as gas (20.9%) and water (13.3%). The elemental composition of the casein tar was: C 66.7%, H 8.3%, N 12.1% and O 12.9% (by difference). The tar sample has been characterised by mass spectrometry, gas chromatography (GC)/MS and heated-probe MS, to give molecular mass distributions for comparison with molecular mass ranges indicated by analytical-scale size-exclusion chromatography (SEC). The tar appeared to be completely soluble in 1-methyl-2-pyrrolidinone (NMP), the solvent used for SEC. It appeared to consist mostly of lower molecular mass fractions with elution times at 18-26 min. GC/MS analysis showed the presence of both aliphatic and aromatic nitrogen-containing components. Neither GC/MS nor heated-probe MS were able to detect more than about half the tar components.     

The influence of dissociation reaction on ammonium nitrate thermal decomposition reaction

In order to investigate the influence of dissociation reaction on thermal decomposition of ammonium nitrate (AN), biochar was selected as an adsorbent to interfere with the dissociation of AN. The TG-DSC results showed that the notable exothermic reaction of AN with the presence of 2% or 7% biochar took place. The decomposition temperature of AN decreased with increasing amount of biochar. The notable knee point was found in the TG curves. The activation energy of AN with biochar in the initial stage was higher than that of AN itself. Remote sensing Fourier transform infrared experiments found biochar induced AN decomposition at about 190 °C, which was also confirmed by the TG-MS results. After dissociation reaction, HNO₃ (g) and NH₃ (g) were adsorbed and crystalline of AN was formed on the surface of biochar. With the increasing temperature, NH₃ escaped from the surface of biochar, while HNO₃ (g) was stayed in biochar. HNO₃ (g) catalyzed the thermal decomposition of AN and also reacted with biochar. The results indicated that dissociation reaction of AN played an important role during AN thermal decomposition process. When dissociation reaction was changed, the thermal decomposition reaction of AN would also change, catalysis or inhibition AN thermal decomposition. It is a useful reference to guide the AN additives selection and to understand the mechanism for the AN decomposition accident.

     

Physicochemical properties evolution of chars from palm kernel shell pyrolysis

To clarify the effect of the pyrolysis operating conditions of the biomass on the physicochemical properties of the char and its combustion reactivity, palm kernel shell was pyrolyzed at different temperatures (400–700 °C). Analyses such as proximate and ultimate analysis, XRD, FTIR, N₂ adsorption, and SEM were used to investigate the physicochemical properties of biochar samples. The results show that an increase in pyrolysis temperature led to a development of pore structure and specific surface area of the produced biochar, which was beneficial for improving the biochar combustion reactivity. Besides, with increase in pyrolysis temperature, the carbon content exhibits a raise trend, but the oxygen and hydrogen contents exhibit the opposite behavior, and the aromaticity and graphitization degree of biochar produced at high temperature also increase. The combustion reactivity of biochar was found to be highly dependent on the pyrolysis temperature, and the aromatic structure and graphitization degree have greater effects on biochar combustion reactivity than those of the specific surface area and pore structure.     

Hydrothermal processing of waste pine wood into industrially useful products

An ongoing major outbreak of mountain pine beetle in Western Canada has provided a clear opportunity to utilize waste pinewood as a source of renewable energy. Therefore hydrothermal processing of waste pinewood as a feedstock for bio-oil and biochar production using subcritical and supercritical water technology was carried out in semi-batch mode to investigate the effect of pressure (200–400 bar) and temperature (300–400 °C) on the yield and composition of bio-oil. The pinewood samples have very high cellulose and hemicellulose content but low ash content and are thus a formidable feedstock for bioenergy production. The optimum conditions for the hydrothermal processing of the pinewood in a tubular reactor were found to be 400 °C and 250 bars with respect to biochar and bio-oil yield based on the highest calorific value analysis. Detailed characterization of bio-oil and biochar was performed using GCMS, NMR, SEM, calorific value, and elemental analysis, respectively. The critical components of bio-oil were found to be phenols, methoxyphenols, hydroxymethyl furfural (HMF), and vanillin, whereas as compared to the raw pine wood, the biochar was considerably lower H:C and O:C ratios than those of the unprocessed pinewood. The analyses of bio-oil by means of GCMS and ¹H NMR showed that it was mainly composed of heterocyclic compounds, phenols, aldehydes and acids.     

Optimization and determination of polycyclic aromatic hydrocarbons in biochar‐based fertilizers

The agronomic benefit of biochar has attracted widespread attention to biochar‐based fertilizers. However, the inevitable presence of polycyclic aromatic hydrocarbons in biochar is a matter of concern because of the health and ecological risks of these compounds. The strong adsorption of polycyclic aromatic hydrocarbons to biochar complicates their analysis and extraction from biochar‐based fertilizers. In this study, we optimized and validated a method for determining the 16 priority polycyclic aromatic hydrocarbons in biochar‐based fertilizers. Results showed that accelerated solvent extraction exhibited high extraction efficiency. Based on a Box–Behnken design with a triplicate central point, accelerated solvent extraction was used under the following optimal operational conditions: extraction temperature of 78°C, extraction time of 17 min, and two static cycles. The optimized method was validated by assessing the linearity of analysis, limit of detection, limit of quantification, recovery, and application to real samples. The results showed that the 16 polycyclic aromatic hydrocarbons exhibited good linearity, with a correlation coefficient of 0.996. The limits of detection varied between 0.001 (phenanthrene) and 0.021 mg/g (benzo[ghi]perylene), and the limits of quantification varied between 0.004 (phenanthrene) and 0.069 mg/g (benzo[ghi]perylene). The relative recoveries of the 16 polycyclic aromatic hydrocarbons were 70.26–102.99%.