Biochar derived from corn stalk and polyethylene co-pyrolysis: characterization and Pb(ii) removal potential

Sustainable management of campus fallen leaves through low-temperature pyrolysis and application in Pb immobilization

Realizing campus sustainability requires the environmental-friendly and economical treatment of tremendous fallen leaves. Producing fallen leaf biochar at a low temperature is a candidate approach. In this study, six common types of fallen leaves on the campus were pyrolyzed at 300 °C. The obtained biochars were characterized and the adsorption mechanisms of lead (Pb) by the fallen leaf biochars were investigated. The adsorption capacity of leaf biochar for Pb was relatively high, up to 209 mg/g (Yulania denudata leaf biochar). Adsorption of Pb onto active sites was the rate-limiting step for most leaf biochars. But for Platanus leaf biochar, intraparticle diffusion of Pb2+ dominated owing to the lowest adsorption capacity. However, the highest exchangeable Pb fraction (27%) indicated its potential for removing aqueous Pb2+. Ginkgo and Prunus cerasifera leaf biochar immobilized Pb by surface complexation and precipitation as lead oxalate. Hence, they were suitable for soil heavy metal remediation. This study shed the light on the sustainable utilization of campus fallen leaves and the application of fallen leaf biochars in heavy metal remediation.

Removal of Cr(VI) from aqueous solution using ball mill modified biochar: multivariate modeling, optimization and experimental study

Chromium (Cr(VI)) pollution has attracted wide attention due to its high toxicity and carcinogenicity. Modified biochar has been widely used in the removal of Cr(VI) in water as an efficient and green adsorbent. However, the existing biochar prepared by chemical modification is usually complicated in process, high in cost, and has secondary pollution, which limits its application. It is urgent to explore modified biochar with simple process, low cost and environmental friendliness. Therefore, ball milling wheat straw biochar (BM-WB) was prepared by ball milling technology in this paper. The adsorption characteristics and mechanism of Cr(VI) removal by BM-WB were analyzed by functional group characterization, adsorption model and response surface method. The results showed that ball milling effectively reduced the particle size of biochar, increased the specific surface area, and more importantly, enhanced the content of oxygen-containing functional groups on the surface of biochar. After ball milling, the adsorption capacity of Cr(VI) increased by 3.5-9.1 times, and the adsorption capacity reached 52.21 mg/g. The adsorption behavior of Cr(VI) follows the pseudo-second-order kinetics and Langmuir isotherm adsorption model rate. Moreover, the Cr(VI) adsorption process of BM-WB is endothermic and spontaneous. Under the optimized conditions of pH 2, temperature 45 °C, and adsorbent dosage 0.1 g, the removal rate of Cr(VI) in the solution can reach 100%. The mechanism of Cr(VI) adsorption by BM-WB is mainly based on electrostatic attraction, redox and complexation. Therefore, ball milled biochar is a cheap, simple and efficient Cr(VI) removal material, which has a good application prospect in the field of remediation of Cr(VI) pollution in water.

Efficiency and mechanism of phosphate adsorption and desorption of a novel Mg-loaded biochar material

Phosphate removal is complicated by the need for resource recovery. Biochar shows promise for efficient phosphate adsorption, but it must be modified to enhance its adsorption capacity. In this work, magnesium (Mg)-loaded biochar was synthesized through a two-step dipping and calcination process, and the MgBC600 product was used to adsorb phosphate from simulated water and biogas slurry wastewater. The phosphate adsorption capacity of Mg-loaded biochar was 109.35 mg/g, which was 12 times higher than that of unmodified biochar. The R2 of the Langmuir and pseudo-second-order kinetic models were 0.988 and 0.990, respectively, which fitted the phosphate adsorption process of MgBC600. Phosphate adsorption by MgBC600 was a spontaneous and endothermic process. The adsorption mechanism study showed that phosphate adsorption was controlled by the formation and electrostatic attraction of MgHPO4. In addition, 98% of chemically adsorbed phosphate was released after regeneration. Using phosphate-adsorbed MgBC600 as a soil amendment, Arabidopsis thaliana was 1.47 times higher than that in the biochar-only group, demonstrating that this is a promising strategy for enhancing phosphate adsorption efficiency and adsorbent recycling.

Tomato waste biochar in the framework of circular economy

Tomato pomace was slowly pyrolyzed at 350 and 550 °C (under an N₂ flow of 50 L/h) at a rate of 6 °C/min and a residence time of 1:30 h to produce two biochars named B350 and B550, respectively. In addition, the two biochars were chemically activated with ΚΟΗ (at a ratio of 1:10 w/v) at 800 °C to produce two new materials named BA350 and BA550. The four biochars produced were characterized physically and chemically (pH, yield, calorific value). They were also analyzed by scanning electron microscopy (SEM), Brunauer-Emmett-Teller (B.E.T), elemental analysis (EA), and thermogravimetric analysis (TGA). The results showed that as the pyrolysis temperature increased (350 to 550 °C), the specific surface area (SSA) increased. The latter was also significantly increased by the activation process. EA showed a variation in the mineral content of the produced biochars, resulting in a different content of the biochars after activation. The parameters studied showed that biochars from tomato waste could be used as an organic amendment to improve soil fertility in agricultural. In addition, because of their ability to absorb water, they could be used as a water reservoir in soils in arid areas.

Value-added biochar production from microwave pyrolysis of peanut shell

In order to seek efficient resource utilization, the carbonization of agricultural and forestry wastes through microwave pyrolysis technology is an important research hotspot to develop value-added products. The main objective is to produce value-added biochar through microwave pyrolysis of peanut shell in this study. The product yields, functional groups, and biochar HHVs caused by pyrolysis temperature (400, 450, 500, 550, and 600 °C), microwave power (350, 450, 550, 650, and 750 W), and residence time (10, 20, 30, 40, and 50 min) were investigated, and the energy recovery efficiencies were evaluated. It was obtained that the biochar yield declined monotonously within the range of 45.3–86.0 wt% with the enhancement of pyrolysis temperature, microwave power, or residence time. The pyrolysis temperature of 400 °C, microwave power of 350 W, and residence time of 10 min generated the maximum biochar yield (86.0 wt%). The value-added biochar was obtained with high HHV (20.15–31.02 MJ/kg) and abundant oxygen-contained functional groups (C–O bonds and C=O bonds). The maximum energy recovery efficiency during the whole process reached 97.96%. The results indicated that the peanut shell could reach high biochar yield through microwave pyrolysis, and potentially be transformed into value-added products with high energy recovery efficiency.

Remediation of heavy metal polluted waters using activated carbon from lignocellulosic biomass: An update of recent trends

The use of a cheap and effective adsorption approach based on biomass-activated carbon (AC) to remediate heavy metal contamination is clearly desirable for developing countries that are economically disadvantaged yet have abundant biomass. Therefore, this review provides an update of recent works utilizing biomass waste-AC to adsorb commonly-encountered adsorbates like Cr, Pb, Cu, Cd, Hg, and As. Various biomass wastes were employed in synthesizing AC via two-steps processing; oxygen-free carbonization followed by activation. In recent works related to the activation step, the microwave technique is growing in popularity compared to the more conventional physical/chemical activation method because the microwave technique can ensure a more uniform energy distribution in the solid adsorbent, resulting in enhanced surface area. Nonetheless, chemical activation is still generally preferred for its ease of operation, lower cost, and shorter preparation time. Several mechanisms related to heavy metal adsorption on biomass wastes-AC were also discussed in detail, such as (i) - physical adsorption/deposition of metals, (ii) - ion-exchange between protonated oxygen-containing functional groups (-OH, -COOH) and divalent metal cations (M²⁺), (iii) - electrostatic interaction between oppositely-charged ions, (iv) - surface complexation between functional groups (-OH, O^2-, -CO-NH-, and -COOH) and heavy metal ions/complexes, and (v) - precipitation/co-precipitation technique. Additionally, key parameters affecting the adsorption performance were scrutinized. In general, this review offers a comprehensive insight into the production of AC from lignocellulosic biomass and its application in treating heavy metals-polluted water, showing that biomass-originated AC could bring great benefits to the environment, economy, and sustainability.

Co-Pyrolysis of Cotton Stalks and Low-Density Polyethylene to Synthesize Biochar and Its Application in Pb(II) Removal

It is inevitable that reclaimed cotton stalks will contain a certain amount of plastic film due to the wide application of plastic mulching during the process of cotton cultivation, and this makes it inappropriate to return it to the field or for it to be processed into silage. In this study, biochars were prepared by the co-pyrolysis of cotton stalk with low-density polyethylene (LDPE) in the proportions of 1:0, 3:1, 2:1, and 1:1 (w/w) at 400 °C, 450 °C, and 500 °C and maintaining them for 1 h. The effects of the co-pyrolysis of cotton stalk with LDPE on the properties of biochars (e.g., pH, yield, elemental analysis, specific surface area, etc.) and the Pb(II) removal capacity were analyzed. Co-pyrolysis cotton stalks with LDPE could delay the decomposition of LDPE but could promote the decomposition of cotton stalk. At 400 °C and 450 °C, the addition of LDPE decreased the H/C ratio, while no significant difference was found between the pristine biochar and the blended biochar pyrolyzed at 500 °C. An FTIR analysis indicated that the surface functional groups of biochar were not affected by the addition of LDPE, except for CH₃ and CH₂. The results of the SEM showed that LDPE could cover the surface of biochar when pyrolyzed at 400 °C, while many macropores were found in the blended biochar that was pyrolyzed at 450 °C and 500 °C, thus increasing its surface area. The blended biochar that was pyrolyzed at 500 °C was more effective in the removal of Pb(II) than the cotton-stalk-derived biochar, which was dominated by monolayer adsorption with a maximum adsorption capacity of approximately 200 mg·g⁻¹. These results suggested that the co-pyrolysis of cotton stalks and LDPE may be used to produce biochar, which is a cost-effective adsorbent for heavy metal removal from aqueous solutions.

A review of prospects and current scenarios of biomass co-pyrolysis for water treatment

With ever-growing population comes an increase in waste and wastewater generated. There is ongoing research to not only reduce the waste but also to increase its value commercially. One method is pyrolysis, a process that converts wastes, at temperatures usually above 300 °C in a pyrolysis unit, to carbon-rich biochars among with other useful products. These chars are known to be beneficial as they can be used for water treatment applications; certain studies also reveal improvements in the biochar quality especially on the surface area and pore volume by imparting thermal and chemical activation methods, which eventually improves the uptake of pollutants during the removal of inorganic and organic contaminants in water. Research based on single waste valorisation into biochar applications for water treatment has been extended and applied to the pyrolysis of two or more feedstocks, termed co-pyrolysis, and its implementation for water treatment. The co-pyrolysis research mainly covers activation, applications, predictive calculations, and modelling studies, including isotherm, kinetic, and thermodynamic adsorption analyses. This paper focuses on the copyrolysis biochar production studies for activated adsorbents, adsorption mechanisms, pollutant removal capacities, regeneration, and real water treatment studies to understand the implementation of these co-pyrolyzed chars in water treatment applications. Finally, some prospects to identify the future progress and opportunities in this area of research are also described. This review provides a way to manage solid waste in a sustainable manner, while developing materials that can be utilized for water treatment, providing a double target approach to pollution management.

Fabrication of Ag3PO4/polyaniline-activated biochar photocatalyst for efficient triclosan degradation process and toxicity assessment

Triclosan (TCS) is a typical environmental pollutant, which seriously threatens the health of humans and organisms. A novel strategy of biochar/Ag₃PO₄/polyaniline (PANI) composite photocatalyst was synthesized by a facile chemical precipitation method to efficiently degrade TCS. XRD, Raman, ESR, etc. were used to reveal the effective associations among physiochemistry, photochemistry and photocatalytic properties of the composite. It was proved the synergistic effects of biochar (T-Bio) and PANI resulted in the decrease of Ag₃PO₄ particle size, the enhancement of adsorption, the improvement of light utilization, the increase of photogenerated carrier separation and the promotion of reactive species. The photocatalytic mechanism showed h⁺ was the main active species, O₂^- and OH played minor roles. Under the irradiation of visible light, the optimal photocatalyst (1.0% T-Bio/AP/1.0% PANI) displayed excellent photocatalytic activity with the removal rate of 85.21% for TCS within 10 min, and the apparent rate constant K' was 2.38 times of Ag₃PO₄. 11 main intermediates for TCS degradation were identified, and their toxicity was significantly reduced. The possible degradation pathways were proposed. This work is the first systematic study on the degradation behavior of TCS by Ag₃PO₄-based photocatalyst, and it provides a new approach to fabricate photocatalysts with synergistic effects and amazing photocatalytic activity by biochar.

Mixed bacteria-loaded biochar for the immobilization of arsenic, lead, and cadmium in a polluted soil system: Effects and mechanisms

The present study explored the immobilization of mixed bacteria-loaded biochar on As, Pb, and Cd was explored. Physisorption and sodium alginate encapsulation were used to synthesize two kinds of mixed bacteria-loaded biochars, referred to as BCM and BCB. The observations of Scanning electron microscope, X-ray diffraction, and Fourier transform infrared spectroscopy distinctly demonstrated the colonization of mixed bacteria on biochar. Besides, the addition of BCM and BCB could increase soil pH with increasing incubation time. The residual fraction of heavy metals and soil dehydrogenase activities were also enhanced after 28 days of incubation. Pb was mainly immobilized by co-precipitation, which meant that Pb could be converted into a consistent crystalline form such as Pb₅(PO₄)₃OH. The X-ray photoelectron spectroscopy and X-ray diffraction analyses of materials identified the formation of Ca₂As₂O₇ and the presence of oxidation from trivalent arsenic to pentavalent arsenic. Cd was adsorbed by forming precipitations (CdCO₃) and exchanging ions with the BCM and BCB. Synergistic reactions between anions and cations also contributed to the immobilization of heavy metals, such as the formation of PbAs₂O₆ and Cd₃(AsO₄)₂. These results confirmed that mixed bacteria-loaded biochar was a feasible technology for the remediation of heavy metals contamination in site soils.

Fabrication and environmental applications of metal-containing solid waste/biochar composites: A review

The resource utilization of industrial solid waste has become a hot issue worldwide. Composites of biochar with metal-containing solid wastes (MCSWs) can not only improve the adsorption performance, but also reduce the cost of modification and promote the recycling of waste resources. Thus, the synthesis and applications of biochar composites modified by MCSWs have been attracting increasing attention. However, different MCSWs may result in metal-containing solid waste/biochar composites (MCSW-BCs) with various physicochemical properties and adsorption performance, causing distinct adsorption mechanisms and applications. Although a lot of researches have been carried out, it is still in infancy. In particular, the explanation on the adsorption mechanisms and influencing factors of pollutant onto MCSW-BCs are not comprehensive and clear enough. Therefore, a systematic review on fabrication and potential environmental applications of different MCSW-BCs is highly needed. Here we summarize the recent advances on the utilization of typical metal-containing solid wastes, preparation of MCSW-BCs, adsorption mechanisms and influencing factors of pollutants by MCSW-BCs as well as their environmental applications. Finally, comments and perspectives for future studies are proposed.

Waste straw derived Mn-doped carbon/mesoporous silica catalyst for enhanced low-temperature SCR of NO

This work proposed a new strategy for the high value utilization of waste straw, in which a Mn-doped carbon/mesoporous silica composite catalyst was prepared by simultaneous utilization of carbon and silicon source from straw for low-temperature denitration. The results showed that the NO conversion rate reached 93% at 180℃ for the composite catalyst with Si/C mass ratio of 35% (Mn/ACMS (35%)). This was significantly higher than those of the activated carbon catalyst (Mn/AC) and mesoporous silica catalyst (Mn/MS), i.e., 58% and 50%, respectively. The SEM images showed that mesoporous silica nanoparticles were dispersed evenly on the carbon surface to form composite materials. XPS results indicated that Mn/ACMS (35%) catalyst showed higher content of chemically adsorbed oxygen (O_α) and Mn⁴⁺ (54.67% and 46.81%) than Mn/AC catalyst (34.38% and 17.49%) and Mn/MS catalyst (32.71% and 30.18%), which was responsible for the improved catalytic activity. Moreover, NH₃-TPD results revealed that Mn/ACMS (35%) had high surface acidity of 6.47 mmol·g^-1, significantly higher than Mn/AC catalyst of 1.51 mmol·g^-1, which was beneficial for adsorbing NH₃. H₂-TPR results suggested that Mn/ACMS (35%) catalyst had much higher H₂ consumption of 1.32 mmol·g^-1 than Mn/AC and Mn/MS catalyst, suggesting better redox performance. The results demonstrated that the straw derived Mn-doped carbon/mesoporous silica composite catalyst can be a potential material for low-temperature denitration.

A Comprehensive Characterization of Different Fractions of Corn Stover and Their Relationships to Multipollutant Sorption Characteristics

Corn stover (CS) is mainly composed of three parts: pith (CSP), rind (CSR), and leaf (CSL). These parts have different lignocellulosic constituents and structural properties. Herein, biosorbents derived from individual corn stover constituents were prepared in an effort to determine the significance of each constituent for multipollutant removal. In this study, SEM, BET, XRD, FTIR, XPS, fibre composition, and contact angle measurements were used to characterize and analyse the physical and chemical properties of the three components of CS and to study their adsorption effects, adsorption isotherms, and kinetics. The lignocellulosic compositions of CSP and CSR were similar, the cellulose content in CSP and CSR was significantly higher than that in CSL, and the hemicellulose content of CSL was much higher than those of CSP and CSR. The minimum lignin content was found in CSP, and the maximum lignin content was found in CSR. The results show that each component had a certain adsorption effect on typical organic pollutants (antibiotics, oils, and dyes). CSP had the strongest oil adsorption capacity, CSR was more suitable for adsorbing antibiotics, and CSL had outstanding adsorption capacity for dye. The pseudo-second-order model and the Langmuir adsorption isotherm model could describe the adsorption processes well, and they consisted of monolayer adsorption accompanied by chemical adsorption reactions. The focus of this study was to provide references for selecting effective adsorbent precursors to remove organic pollutants from wastewater.