Sorption behaviour of xylene isomers on biochar from a range of feedstock

Agri-food waste biosorbents for volatile organic compounds removal from air and industrial gases - A review

Approximately 1.3 billion metric tons of agricultural and food waste is produced annually, highlighting the need for appropriate processing and management strategies. This paper provides an exhaustive overview of the utilization of agri-food waste as a biosorbents for the elimination of volatile organic compounds (VOCs) from gaseous streams. The review paper underscores the critical role of waste management in the context of a circular economy, wherein waste is not viewed as a final product, but rather as a valuable resource for innovative processes. This perspective is consistent with the principles of resource efficiency and sustainability. Various types of waste have been described as effective biosorbents, and methods for biosorbents preparation have been discussed, including thermal treatment, surface activation, and doping with nitrogen, phosphorus, and sulfur atoms. This review further investigates the applications of these biosorbents in adsorbing VOCs from gaseous streams and elucidates the primary mechanisms governing the adsorption process. Additionally, this study sheds light on methods of biosorbents regeneration, which is a key aspect of practical applications. The paper concludes with a critical commentary and discussion of future perspectives in this field, emphasizing the need for more research and innovation in waste management to fully realize the potential of a circular economy. This review serves as a valuable resource for researchers and practitioners interested in the potential use of agri-food waste biosorbents for VOCs removal, marking a significant first step toward considering these aspects together.

Performance and mechanism of benzene adsorption on ZnCl2 one-step modified corn cob biochar

Utilizing cost-effective corn cob, zinc chloride-modified biochar was synthesized through one-step method for benzene adsorption from air. Study on impregnation ratio impact showed optimal benzene adsorption at ZnCl2:CC ratio of 1.5:1, with capacity reaching 170.53 mg g-1. Characterization using BET, SEM, FTIR, and XPS was conducted. BET results indicated specific surface area of Zn1.5BC at 1260.63 m2 g-1 and maximum pore volume of 0.546 m3 g-1. SEM analysis revealed microporous-mesoporous structure in Zn1.5BC, marking significant improvement over original biomass. DFT pore size distribution and FTIR analysis suggested post-modification dehydration and elimination reactions, leading to volatile compound release, functional group reduction, and pore widening. XPS analysis showed decrease in O = C-OH content with increased impregnation ratio, enhancing biochar's π-π electron diffusion for benzene. Langmuir isotherm and pseudo-second-order kinetic models effectively described experimental data, indicating multilayer benzene adsorption on biochar controlled by complex physicochemical adsorption and pore diffusion. Adsorption condition assessment, including adsorption temperature (20-120 ℃) and benzene concentration in inlet phase (159.73-383.36 mg L-1), was performed. Yoon-Nelson model fitting indicated adsorption site loss at higher temperatures and reduced capture ability due to increased adsorbate molecule kinetic energy. Higher adsorbate concentrations aided adsorption molecule diffusion to biochar surface and internal pores, increasing adsorption rate and shortening equilibrium time. Overall, zinc chloride-modified biochar facilitates benzene adsorption through pore filling and π-π interactions, with pore filling as primary mechanism. Produced biochar shows excellent regeneration properties and reusability.

Disintegration of biochar adsorbent under the hydraulic conditions of fixed bed water treatment

Recent studies have provided promising evidence for potential applications of biochar in environmental engineering, including its use as an alternative carbonaceous adsorbent for water and wastewater treatment. Carbonaceous adsorbents, such as activated carbon and biochar, are prone to disintegration and erosion due to water flow, potentially leading to the co-transport of hazardous contaminants with eroded fine particles (1 μm or smaller). Despite its significance in overall performance assessment, the stability and erodibility of biochar as an adsorbent in fixed bed water treatment have received limited research attention. This paper presents the results of a series of filtration tests and microscopic examinations to evaluate the disintegration of activated carbon and three types of biochar filters under the hydraulic conditions of fixed bed filtration. A novel testing design was employed to study the effects of fluid velocities and ionic strengths on disintegration, mass loss, and the morphology of granular adsorbents before and after water flushing. The results indicate that disintegration of both activated carbon and biochar is continuous but exhibits different behaviour with pore volume. Although fluid velocity influenced erosion rates, minimal differences were observed in overall mass loss. Ionic strength had a more pronounced impact on the erodibility and stability of particles in suspension by altering electrical conductivity and Zeta potential. Disintegration of hardwood biochar was found to be comparable to that of activated carbon; however, impurities in biochar (elements other than carbon and oxygen) are more likely to be flushed out, creating additional pathways for co-transport of contaminants.

Aging affects isomer-specific occurrence of dechlorane plus in soil profiles: A case study in a geographically isolated landfill from the Tibetan Plateau

Two major structural isomers in commercial dechlorane plus (DP) mixtures, anti-DP and syn-DP, generally displayed varied desorption and partitioning efficiencies in soils, which may be linked to their different aging rates. However, the molecular parameters that govern the degree of aging and its associated effects on the occurrence of DP isomers have not been comprehensively investigated. In this study, the relative abundance of rapid desorption concentration (R_rapid) was measured for anti-DP, syn-DP, anti-Cl₁₁-DP, anti-Cl₁₀-DP, Dechlorane-604 (Dec-604), and Dechlorane-602 (Dec-602) at a geographically isolated landfill area in the Tibetan Plateau. The R_rapid values were used as an indicator of aging degree, exhibiting a close correlation with the three-dimension conformation of the molecules for the dechlorane series compounds. This observation suggested that planar molecules may have a greater tendency to accumulate in the condensed phase of organic matter and undergo more rapid aging. The fractional abundances and dechlorinated products of anti-DP were found to be predominantly controlled by the aging degree of DP isomers. The multiple nonlinear regression model indicated that differences in aging between anti-CP and syn-DP were primarily driven by the total desorption concentration and soil organic matter content. Aging plays a significant role in both the transport processes and metabolism of DP isomers and should be taken into account to refine the assessment of their environmental behaviors.

Biochar enhanced organic matter transformation during pig manure composting: Roles of the cellulase activity and fungal community

Fungal degradation of cellulose is a key step in the conversion of organic matter in composting. This study investigated the effects of adding 10% biochar (including, prepared from corn stalk and rape stalk corresponding to CSB and RSB) on organic matter transformation in composting and determined the role of cellulase and fungal communities in the conversion of organic matter. The results showed that biochar could enhance the conversion of organic matter, especially in RSB treatment. Biochar could increase cellulase activity, and RSB could enhance 33.78% and 30.70% the average activity of cellulase compared with the control and CSB treatments in the mesophilic to thermophilic phase, respectively. The results of high throughput sequencing demonstrated that Basidiomycota dominant in mesophilic phase, and Ascomycota dominant in other phases of composting. The redundancy analysis showed that Alternaria, Thermomycees, Aspergillus, Wallemia, and Melanocarpus might be the key fungi for the degradation of organic matter, and Fusarium, Penicillium, and Scopulariopsis may promote the conversion of organic matter. Network showed that the addition of RSB changed the interactions between fungal communities and organic matter transformation, and RSB treatment enriched members of Ascomycota related to organic matter transformation and cellulase activity. These results indicated that RSB improved organic matter conversion by enhancing the role of cellulase and fungal communities.

Microwave-assisted pyrolysis derived biochar for volatile organic compounds treatment: Characteristics and adsorption performance

Biochar derived from corn stalk doping with activated carbon was produced by microwave-assisted pyrolysis and applied to sorb volatile organic compounds (VOCs: benzene and o-xylene). Specific surface area (SSA), total pore volume (TPV) and micropore volume (MV) of microwave biochar increased with increasing microwave power with the maximum values 325.2 m²·g^-1, 0.181 mL·g^-1 and 0.1420 mL·g^-1, respectively. Adsorption capacities of benzene and o-xylene on microwave biochar ranged 6.82-54.75 mg·g^-1 and 7.43-48.73 mg·g^-1, which were separate positively related with SSA, TPV, and MV. Benzene adsorption was mainly dominated by surface interaction and partition mechanisms, while o-xylene adsorption was governed by pore filling. The adsorption capacities of microwave biochar for benzene and o-xylene decreased by only 0.30% and 0.99% on the 5th cycle that illustrated the reasonably good reusability of microwave biochar. The results of this research demonstrate that microwave biochar is a promising adsorbent for VOCs removal.

Mechanistic insights into ball milling enhanced montmorillonite modification with tetramethylammonium for adsorption of gaseous toluene

Montmorillonite is widely used for pollutants adsorption due to its porous structure and low price. However, the low specific surface area and small porosity limit its application in gas adsorption field. In this study, montmorillonite was organically modified using a facile dry ball milling method by tetramethylammonium bromide. The adsorption behaviour of toluene as a model VOC compound on organic montmorillonite was systematically investigated through adsorption breakthrough curves, adsorption kinetics and isotherms. After modification by ball milling, the specific surface area of ball milling with tetramethylammonium bromide for montmorillonite modification (BMTMt) was increased from 20.6 m²/g to 186.4 m²/g, and the microporosity proportion was up to 47%. Dynamic adsorption experiments showed that the best performance of BMTMt for toluene (55.9 mg/g) was 6 times higher than that of original montmorillonite (8.8 mg/g). Compared with the water bath preparation method, ball milling method promoted the intercalation of tetramethylammonium bromide into the layers of montmorillonite, resulting in a higher proportion of micropores. Density functional theory calculations indicated that the interaction between tetramethylammonium bromide and montmorillonite was mainly electrostatic forces, and the enhanced adsorption performance for toluene was mainly through microporous filling. BMTMt was proved to be a promising adsorbent for VOCs removal.

Electroactive Fe-biochar for redox-related remediation of arsenic and chromium: Distinct redox nature with varying iron/carbon speciation

Electroactive Fe-biochar has attracted significant attention for As(III)/Cr(VI) immobilization through redox reactions, and its performance essentially lies in the regulation of various Fe/C moieties for desired redox performance. Here, a series of Fe-biochar with distinct Fe/C speciation were rationally produced via two-step pyrolysis of iron minerals and biomass waste at 400-850 °C (BCX-Fe-Y, X and Y represented the first- and second-step pyrolysis temperature, respectively). The redox transformation of Cr(VI) and As(III) by Fe-biochar was evaluated in simulated wastewater under oxic or anoxic conditions. Results showed that more effective Cr(VI) reduction could be achieved by BCX-Fe-400, while a higher amount of As (III) was oxidized by BCX-Fe-850 under the anoxic environment. Besides, BCX-Fe-400 could generate more reactive oxygen species (e.g.,^•OH) by reducing the O₂, which enhanced the redox-related transformation of pollutants under the oxic situation. The evolving redox performance of Fe-biochar was governed by the transition of the redox state from reductive to oxidative related to the Fe/C speciation. The small-sized amorphous/low-crystalline ferrous minerals contributed to a higher electron-donating capacity (0.43-1.28 mmol g^-1) of BCX-Fe-400. In contrast, the oxidative surface oxygen-functionalities (i.e., carboxyl and quinoid) on BCX-Fe-850 endowed a stronger electron-accepting capacity (0.71-1.39 mmol g^-1). Moreover, the graphitic crystallites with edge-type defects and porous structure facilitated the electron transfer, leading to a higher electron efficiency of BCX-Fe-850. Overall, we unveiled the roles of both Fe and C speciation in maneuvering the redox reactivity of Fe-biochar, which can advance our rational design of electroactive Fe-biochar for redox-related environmental remediation.

Competitive adsorption of multicomponent volatile organic compounds on biochar

Crude oil contaminated lands are recognised to have significant contributions to airborne volatile organic compounds (VOCs) with adverse effects on human health and tropospheric ozone. Soil capping systems for controlling harmful emissions are critical engineering solutions where advanced soil remediation techniques are neither available nor feasible. Studies on the adsorption of single VOC species in biochar have shown promising results as a potential capping material; however, current understanding of mixed gas system and multi-component adsorption of VOCs on biochar which would represent more realistic in situ conditions is very limited. We present, for the first time, the results of a study on competitive adsorption of mixed VOCs, including aromatic and non-aromatic VOCs commonly emitted from crude oil contaminated sites on two types of biochar pyrolysed at 500°C from wheat straw and bagasse as feedstock. The kinetics of sorption of multicomponent VOCs including acetone, hexane, toluene and p-xylene in biochar are studied based on the results of an extensive experimental investigation using a bespoke laboratory setup. Both biochar types used in this study presented a high sorption capacity for VOC compounds when tested individually (51-110 mg/g). For the multicomponent mixture, the competition for occupying sorption sites on biochar surface resulted in a lower absolute sorption capacity for each species, however, the overall sorption capacity of biochar remained more or less similar to that observed in the single gas experiments (50-109 mg/g). The chemical interactions via hydrogen bonds, electrostatic attraction, and pore-filling were found to be the main mechanisms of adsorption of VOC in the biochar studied. The efficiency of biochar regeneration was assessed through five cycles of adsorption-desorption tests and was found to be between 88% and 96%. The incomplete desorption observed confirm the formation of likely permanent bonds and heel build-ups during the sorption process.

Recent Progress in Metal-Organic Framework-Derived Nanostructures in the Removal of Volatile Organic Compounds

Air is the most crucial and life-supporting input from nature to the living beings of the planet. The composition and quality of air significantly affects human health, either directly or indirectly. The presence of some industrially released gases, small particles of anthropogenic origin, and the deviation from the normal composition of air from the natural condition causes air pollution. Volatile organic compounds (VOCs) are common contaminants found as indoor as well as outdoor pollutants. Such pollutants represent acute or chronic health hazards to the human physiological system. In the environment, such polluted gases may cause chemical or photochemical smog, leading to detrimental effects such as acid rain, global warming, and environmental pollution through different routes. Ultimately, this will propagate into the food web and affect the ecosystem. In this context, the efficient removal of volatile organic compounds (VOCs) from the environment remains a major threat globally, yet satisfactory strategies and auxiliary materials are far from being in place. Metal–organic frameworks (MOFs) are known as an advanced class of porous coordination polymers, a smart material constructed from the covalently bonded and highly ordered arrangements of metal nodes and polyfunctional organic linkers with an organic–inorganic hybrid nature, high porosities and surface areas, abundant metal/organic species, large pore volumes, and elegant tunability of structures and compositions, making them ideal candidates for the removal of unwanted VOCs from air. This review summarizes the fundamentals of MOFs and VOCs with recent research progress on MOF-derived nanostructures/porous materials and their composites for the efficient removal of VOCs in the air, the remaining challenges, and some prospective for future efforts.

A mechanistic study on removal efficiency of four antibiotics by animal and plant origin precursors-derived biochars

Extensive research has been performed on the utilization of biochar for pollutant removal via sorption. Additionally, the relationship between sorption strength of organic pollutants by organic matter and nanomaterials and their sorption site energy distribution has been studied. However, the linkage between removal efficiency of organic pollutants and the sorption site energy distribution on biochars is unknown. As a first attempt to address this knowledge gap, three biochars were derived from two plant-origin precursors (corn straw-CS; birch sawdust-BS) and one animal-origin precursor (meat and bone meal-MBM) at 500 °C (CS-500, BS-500, and MBM-500). In addition, two biochars were prepared with CS at 300 and 800 °C (CS-300 and CS-800) to examine the relationship between their site energy distribution and removal efficiency of antibiotics including sulfadiazine (SDZ), sulfamethoxazole (SMX), tetracycline (TC) and ciprofloxacin (CFX) by these materials. Our findings showed that the antibiotic-biochar interactions can be well interpreted with site energy distribution and XPS analysis results. Polar interactions between CS-300, CS-500, and CS-800 and SDZ and SMX occurring at the high-energy sites dominated their removal. However, TC and CFX removal by these biochars was driven by their polar interactions occurring at high-energy sites and π-π interactions at low-energy sites. The π-π stacking mechanism tended to dominate their removal with increasing charring temperature. Abundance of polar functionalities on CS-500, BS-500, and MBM-500 and TC removal efficiency of these materials consistently followed an order of MBM-500 > CS-500 > BS-500, highlighting importance of precursors for making biochars and polar interactions in its removal.