Surface modified and activated waste bone char for rapid and efficient VOCs adsorption

Review on the impact of heavy metals from industrial wastewater effluent and removal technologies

The incidence of water pollution in developing countries is high due to the lack of regulatory policies and laws that protect water bodies from anthropogenic activities and industrial wastewater. Industrial wastewater contains significant amounts of heavy metals that are detrimental to human health, aquatic organisms, and the ecosystem. The focus of this review was to evaluate the sources and treatment methods of wastewater, with an emphasis on technologies, advantages, disadvantages, and innovation. It was observed that conventional methods of wastewater treatment (such as flotation, coagulation/flocculation, and adsorption) had shown promising results but posed certain limitations, such as the generation of high volumes of sludge, relatively low removal rates, inefficiency in treating low metal concentrations, and sensitivity to varying pH. Recent technologies like nanotechnology, photocatalysis, and electrochemical coagulation have significant advantages over conventional methods for removing heavy metals, including higher removal rates, improved energy efficiency, and greater selectivity for specific contaminants. However, the high costs associated with these advanced methods remain a major drawback. Therefore, we recommend that future developments in wastewater treatment technology focus on reducing both costs and waste generation.

Seafood waste derived carbon nanomaterials for removal and detection of food safety hazards

Nanobiotechnology and the engineering of nanomaterials are currently the main focus of many researches. Seafood waste carbon nanomaterials (SWCNs) are a renewable resource with large surface area, porous structure, high reactivity, and abundant active sites. They efficiently adsorb food contaminants through π-π conjugated, ion exchange, and electrostatic interaction. Furthermore, SWCNs prepared from seafood waste are rich in N and O functional groups. They have high quantum yield (QY) and excellent fluorescence properties, making them promising materials for the removal and detection of pollutants. It provides an opportunity by which solutions to the long-term challenges of the food industry in assessing food safety, maintaining food quality, detecting contaminants and pretreating samples can be found. In addition, carbon nanomaterials can be used as adsorbents to reduce environmental pollutants and prevent food safety problems from the source. In this paper, the types of SWCNs are reviewed; the synthesis, properties and applications of SWCNs are reviewed and the raw material selection, preparation methods, reaction conditions and formation mechanisms of biomass-based carbon materials are studied in depth. Finally, the advantages of seafood waste carbon and its composite materials in pollutant removal and detection were discussed, and existing problems were pointed out, which provided ideas for the future development and research directions of this interesting and versatile material. Based on the concept of waste pricing and a recycling economy, the aim of this paper is to outline current trends and the future potential to transform residues from the seafood waste sector into valuable biological (nano) materials, and to apply them to food safety.

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.

Biochar as an effective material for acetone sorption and the effect of surface area on the mechanism of sorption

Walnut shells and apricot pits were used to produce non-activated, air-activated and steam-activated biochar. The specific surface area decreased in the order steam-activated (500-727 m 2.g-1), air-activated (59-514 m2.g-1) and non-activated biochars (1.71-236 m2.g-1). The results indicated that water steam created a multi-layer block structure with a well-developed porous structure, especially at 900 °C, while activation with air resulted in a more fragmented structure with a higher amount of coarse pores, leading to lower specific surface values. Acetone sorption experiments were performed in order to determine the acetone sorption capacity and to evaluate the acetone sorption kinetics of the biochars, as well as to identify the possible mechanism of sorption. The maximum sorption capacity estimated from the adsorption isotherms up to a relative pressure of 0.95 ranged from 60.3 to 277.3 mg g-1, and was highest in the steam-activated biochar with the largest surface area. The acetone adsorption isotherms were fitted with different adsorption models, where the Fritz-Schlunder model showed the best fitting results. The adsorption kinetics was evaluated using two kinetics models - pseudo first order and pseudo second order. The results indicated that the biochars with a large surface area exhibited physical sorption through van der Waals forces as the dominant mechanism, while acetone sorption on samples with a smaller surface area can be attributed to a mixed dual sorption mechanism, which combines physical sorption and chemisorption on oxygen functional groups. The perfect reusability of the biochars was confirmed by four consecutive adsorption-desorption cycles.

A new attempt to control volatile organic compounds (VOCs) pollution - Modification technology of biomass for adsorption of VOCs gas

The detrimental impact of volatile organic compounds on the surroundings is widely acknowledged, and effective solutions must be sought to mitigate their pollution. Adsorption treatment is a cost-effective, energy-saving, and flexible solution that has gained popularity. Biomass is an inexpensive, naturally porous material with exceptional adsorbent properties. This article examines current research on volatile organic compounds adsorption using biomass, including the composition of these compounds and the physical (van der Waals) and chemical mechanisms (Chemical bonding) by which porous materials adsorb them. Specifically, the strategic modification of the surface chemical functional groups and pore structure is explored to facilitate optimal adsorption, including pyrolysis, activation, heteroatom doping and other methods. It is worth noting that biomass adsorbents are emerging as a highly promising strategy for green treatment of volatile organic compounds pollution in the future. Overall, the findings signify that biomass modification represents a viable and competent approach for eliminating volatile organic compounds from the environment.

Synthesis of Porous Activated Carbon Doped with Tetramethylammonium Hydroxide: Evaluation of Excellent Gasoline Vapor Adsorption Performance and Activation Mechanism

The rapid urbanization and industrialization in China have led to an urgent dilemma for controlling urban air pollution, including the intensified emission of gasoline vapor into the atmosphere. Herein, we selected highland barley straw as a raw material and KOH and tetramethylammonium hydroxide (TMAOH) as activators to synthesize nitrogen-doped layered porous carbon (K-thAC) by a three-step activation method. The obtained K-thAC materials had a high specific surface area, reaching 3119 m2/g. Dynamic adsorption experiments demonstrated a superior adsorption capacity of up to 501 mg/g (K-thAC-25) for gasoline vapor compared with other documented carbon adsorbents. Moreover, adjusting the ratio of raw materials with a series of active ingredients could further improve the pore properties of the obtained K-thACs and their adsorption performance for gasoline vapor. Furthermore, the K-thAC materials were also characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), synchronous thermogravimetry (STA), X-ray powder diffraction (XRD), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption tests. This study synthesized a novel plant-based material to treat gasoline vapor pollution efficiently.

Recent advances in the control of volatile organic compounds emissions from indoor wood-based panels: A comprehensive review

Wood-based panels provide efficient alternatives to materials such as plastics derived from traditional petroleum sources and thereby help to mitigate greenhouse gas emissions. Unfortunately, using indoor manufactured panel products also results in significant emissions of volatile organic compounds including olefins, aromatic and ester compounds, which negatively affect human health. This paper highlights recent developments and notable achievements in the field of indoor hazardous air treatment technologies to guide future research toward environmentally friendly and economically feasible directions that may have a significant impact on the improvement of human settlements. Summarizing and synthesizing the principles, advantages, and limitations of different technologies can assist policymakers and engineers in identifying the most appropriate technology for a particular air pollution control program based on criteria such as cost-effectiveness, efficiency, and environmental impact. In addition, insights into the development of indoor air pollution control technologies are provided and potential areas for innovation, improvement of existing technologies, and development of new technologies are identified. Finally, the authors also hope that this sub-paper will raise public awareness of indoor air pollution issues and promote a better understanding of the importance of indoor air pollution control technologies for public health, environmental protection, and sustainable development.

Preparation, characterisation and applications of bone char, a food waste-derived sustainable material: A review

The production of increasing quantities of by-products is a key challenge for modern society; their valorisation - turning them into valuable compounds with technological applications - is the way forward, in line with circular economy principles. In this review, the conversion of bones (by-products of the agro-food industry) into bone char is described. Bone char is obtained with a process of pyrolysis, which converts the organic carbon into an inorganic graphitic one. Differently from standard biochar of plant origin, however, bone char also contains calcium phosphates, the main component of bone (often hydroxyapatite). The combination of calcium phosphate and graphitic carbon makes bone char a unique material, with different possible uses. Here bone chars' applications in environmental remediation, sustainable agriculture, catalysis and electrochemistry are discussed; several aspects are considered, including the bones used to prepare bone char, the preparation conditions, how these affect the properties of the materials (i.e. porosity, surface area) and its functional properties. The advantages and limitations of bone chars in comparison to traditional biochar are discussed, highlighting the directions the research should take for bone chars' performances to improve. Moreover, an analysis on the sustainability of bone chars' preparation and use is also included.

Chicken Cartilage-Derived Carbon for Efficient Xylene Removal

Chicken cartilage was used for the first time as a raw material for the microwave-assisted synthesis of biochar and activated carbon. Various microwave absorbers, i.e., commercial active carbon, scrap tyres, silicon carbide, and chicken bone-derived biochar, as well as various microwave powers, were tested for their effect on the rate of pyrolysis and the type of products formed. Biochars synthesised under 400 W in the presence of scrap tyres and chicken bone-derived biochar were activated with KOH and K₂CO₃ with detergent to produce activated carbon with a highly developed porous structure that would be able to effectively adsorb xylene vapours. All carbons were thoroughly characterised (infrared spectroscopy, X-ray fluorescence spectrometry, nitrogen adsorption/desorption, Raman spectroscopy, proximate and ultimate analysis) and tested as xylene sorbents in dynamic systems. It was found that the activation causes an increase of up to 1042 m²·g^-1 in the specific surface area, which ensures the sorption capacity of xylene about 300 mg·g^-1. Studies of the composition of biogas emitted during pyrolysis revealed that particularly valuable gaseous products are formed when pyrolysis is carried out in the presence of silicon carbide as a microwave absorber.

Agricultural waste to real worth biochar as a sustainable material for supercapacitor

Biochar made from agricultural waste is gaining more attention in energy field due to its sustainability, low cost, apart from having high supercapacitance performance. Also, it has a wide range of environmental applications, including wastewater treatment, upgrading soil fertility, contaminant immobilization, and in situ carbon sequestration. The existing thermo-chemical methodologies for converting agricultural waste into a sustainable material i.e. biochar and the role of activation agents in enhancing the performance of these materials were critically analyzed and discussed. An overview of recent trends in agricultural waste-derived biochar for supercapacitor electrodes is highlighted in this review that emphasizes green circular economy for encouraging net-zero utility of agriculture waste biomass. The roles of various newly prepared "green" electrolytes in reducing the negative consequences of supercapacitor is also reviewed. The trashing of agricultural waste and the depletion of energy supplies has become a global concern, hurting the world's ecosystem and economy through pollution and a fuel crisis and hence the concept of a green circular economic model is also highlighted.

Biomass Derived, Hierarchically Porous, Activated Starbons® as Adsorbents for Volatile Organic Compounds

The use of potassium hydroxide activated Starbons® derived from starch and alginic acid as adsorbents for 29 volatile organic compounds (VOCs) was investigated. In every case, the alginic acid derived Starbon (A800K2) was found to be the optimal adsorbent, significantly outperforming both commercial activated carbon and starch derived, activated Starbon (S800K2). The saturated adsorption capacity of A800K2 depends on both the size of the VOC and the functional groups it contains. The highest saturated adsorption capacities were obtained with small VOCs. For VOC's of similar size, the presence of polarizable electrons in lone pairs or π-bonds within non-polar VOCs was beneficial. Analysis of porosimetry data suggests that the VOC's are being adsorbed within the pore structure of A800K2 rather than just on its surface. The adsorption was completely reversible by thermal treatment of the saturated Starbon under vacuum.

Precise preparation of biomass-based porous carbon with pore structure-dependent VOCs adsorption/desorption performance by bacterial pretreatment and its forming process

Pore distribution characteristic is one of the most crucial factors for porous adsorption materials, and the variety of volatile organic compounds (VOCs) approaches about how to simply and accurately tailor practical porous carbons for VOCs adsorption has gradually attracted attention. Here, precursors with different lignocellulose mass ratios have been used to produce porous carbon for model experiments to investigate the influence of the precursor lignocellulose contents on the pore structure and distribution characteristics of porous carbon, and the applicability of these mechanisms to real biomass materials has been further verified through bacteria-targeted bagasse decomposition: the microvolumes of ultra-micropores have decreased with decrease in cellulose contents, while mesopores have followed the reverse trend. The dynamic toluene adsorption/desorption performances of the obtained samples have been tested. The BACs-36 exhibits high toluene adsorption performance in low concentration with 635 mg/g while the BACs-48 shows excellent reusability in 10 times cycles. Based on this the balance between the adsorptive and regenerative capacities has been observed which indicates that carbon materials with abundant micropores and narrow mesopores have much better adsorption performance than porous carbon with a hierarchical pore structure, while the latter show better regeneration abilities than the former, which resulting in less desorption as a counter-acting force at the pore wall. Furthermore, the porous carbon has been shaped by one-step co-pyrolysis method using phenolic resin, which can not only maintain the hardness but also can avoid pore plugging phenomenon.

Adsorption of multicomponent VOCs on various biomass-derived hierarchical porous carbon: A study on adsorption mechanism and competitive effect

Biomass-derived porous carbon materials are potential adsorbents for VOCs. In this work, biomass-derived nitrogen-doped hierarchical porous carbons (NHPCs) were synthesized by a one-step pyrolysis activation combined with nitrogen doping method from several biomass wastes (corn straw, wheat stalk, bamboo, pine, and corncob). NHPCs have a hierarchical porous structure with micro-meso-macropores distribution, nitrogen doping, large specific surface area, and pore volume. The corncob derived carbon (NHPC-CC) has the best activation result as analyses showed that a lower ash content and higher total cellulose composition content of the biomass result in a better pore activation effect. Single and multi-component dynamic adsorption tests of typical VOCs (benzene, toluene, and chlorobenzene) were conducted on NHPCs in laboratory conditions (∼500 ppm). Promising VOC adsorption capacity and great adsorption kinetics with low mass transfer resistance were found on NHPCs. Correlation analysis showed that the high VOC adsorption capacity and great adsorption kinetics can be attributed to the large surface area of micro-mesopores and the mass transfer channels provided by meso-macropores respectively. The competitive dynamic adsorption tests revealed that the VOC with lower saturated vapor pressure has more adsorption sites on the surface of micro-mesopores and stronger adsorption force, which results in the higher adsorption capacity and desorption caused by substitution reaction in VOCs competitive adsorption process. In detail, the process of toluene and chlorobenzene competitive adsorption was described. Besides, well recyclability of NHPC-CC was revealed as the VOCs adsorption capacity reductions were less than 10% after four adsorption-desorption cycles. All studies showed that the NHPC-CC could be potential adsorbent for VOCs in industrial process.

Evaluation of HKUST-1 as Volatile Organic Compound Adsorbents for Respiratory Filters

Cyclohexane is a representative of volatile organic compounds (VOCs). VOCs can cause serious health problems in case of continuous exposure; therefore, it is essential to develop efficient personal protective equipment. Historically, activated carbons are used as VOC adsorbents. However, the emergence of promising novel adsorbents, such as metal-organic frameworks, has pushed the research to study their behavior under the same conditions. In this work, the use of the well-known HKUST-1 MOF of different particle sizes (20 μm, 300-600 μm, and 1-1.18 mm) for the adsorption of low-grade (5000 ppm) cyclohexane combined with different water concentrations (dry, 27 and 80% RH) in a fixed bed is proposed. The results were compared under the same conditions for a typically used activated carbon, PICACTIF TA 60. HKUST-1 has higher affinity to cyclohexane than PICACTIF for the whole pressure range studied, especially at low partial pressures. It begins to adsorb much earlier (0.0025 kPa) than the activated carbon (0.01 kPa). However, a different adsorption behavior is evidenced for both materials in the presence of water vapor since HKUST-1 is very hydrophilic in the zone near to the copper open metal sites, whereas PICACTIF is hydrophobic. After three consecutive cycles, good stability results were obtained for the MOF, comparable to activated carbon, even in the presence of water. As the main finding, although the unstability of HKUST-1 is well established under high humid conditions, the kinetic of degradation has not been established so far. Here, it is shown that the time usage of HKUST-1 as the adsorbent for respiratory mask (single pass) is not affected by the degradation of the structure, which may occur on a longer time scale. Finally, shaping by tableting provides good results since it is possible to increase the MOF density by around 69% with minor loss of adsorption capacity. The best fraction is 300-600 μm, reaching cyclohexane breakthrough times around 85 min/cm³ at 80% RH, comparable with PICACTIF-activated carbon and promising for practical applications.

Performance evaluation of activated carbon sorbents for indoor air purification during normal and wildfire events

Volatile organic compounds (VOCs) are a significant class of indoor air pollutants and are known for their adverse effects on health. A common strategy to reduce indoor VOC levels is to use sorbents, including activated carbons (ACs). The amount of activated carbon is critical to achieving a reasonable AC filter lifetime in an air purification device. The study aims to estimate the amount of carbon needed in a typical indoor environment and in a heavy use setting such as during cooking, agriculture field fires, or wildfires. The problem is complex as various types of ACs are used, and the type and concentration of VOCs in the indoor environment also vary in different settings. Therefore, literature data on thermophysical parameters for 45 AC-VOC pairs was used to estimate the required amount of AC under a given set of conditions. The study uses modeling distributions of the footprint of suitable carbon filters for the removal of common VOCs encountered indoors for a period of 30 days. It was found that while 50% of AC-VOC pairs surveyed will require about 190-370 g at low indoor VOCs levels of 0.1-1 μmol/m³(considered a good clean indoor environment), up to 1.1 kg of ACs are needed for a carbon filter to survive 30 days in a typical indoor environment (VOCs levels of 10 μmol/m³). On the other hand, 3-15 kg or more AC will be needed in a filter to survive 30 days during adverse events such as wildfires. The objective of the present study is to aid consumers and businesses in making an informed decision on the type of AC-based indoor air filters that meet their needs. Using this data, an open-access online calculator is being developed to predict the amount of carbon needed in a filter/device at any specific indoor air condition.

Fe/C materials prepared by one-step calcination of acidified municipal sludge and their excellent adsorption of Cr(VI)

Biochar derived from municipal sludge can be applied to adsorption. But it usually requires activation and pickling due to the generation of impurities such as metal oxide particles, which is uneconomical. Here, a facile strategy, acidification-one-step calcination, was developed and sludge-based Fe-C materials with good Cr(VI) removal effect were obtained by regulating the amount of hydrochloric acid. The results show that the adsorption capacity of Fe/C-5 (the best sample) for Cr(VI) was 150.84 mg g^-1. According to the Langmuir isotherm and pseudo-second-order kinetic model, the removal of Cr(VI) by Fe/C-5 is spontaneous and endothermic chemisorption process. In addition, Fe/C-5 has good ability to remove Cr(VI) under the interference of coexisting ions, and has good cycle stability. The removal of Cr(VI) by Fe/C-5 is considered to be synergistic process of adsorption and reduction. The Fe atoms were highly dispersed in Fe/C-5 and tightly bonded with C atoms, which not only strengthened the Cr(VI) adsorption by electrostatic attraction, but also activated the C atoms in the biochar material, so that the C atoms can reduce Cr(VI) to Cr(III) under acidic conditions. This may be due to the fact that acid pretreatment converted the iron in municipal sludge in the form of Fe-O/OH to free Fe³⁺ and entered the C lattice during the calcination process. In this work, Fe-C materials with excellent Cr(VI) adsorption capacity were prepared by one-step calcination method, which has important reference significance for the resource utilization of municipal sludge.

Value-added materials recovered from waste bone biomass: technologies and applications

As the world population increases, the generation of waste bones will multiply exponentially, increasing landfill usage and posing health risks. This review aims to shed light on technologies for recovering valuable materials (e.g., alkaline earth material oxide such as CaO, hydroxyapatite, beta tri-calcium phosphate, phosphate and bone char) from waste bones, and discuss their potential applications as an adsorbent, catalyst and catalyst support, hydroxyapatite for tissue engineering, electrodes for energy storage, and phosphate source for soil remediation. Waste bone derived hydroxyapatite and bone char have found applications as a catalyst or catalyst support in organic synthesis, selective oxidation, biodiesel production, hydrocracking of heavy oil, selective hydrogenation and synthesis of bioactive compounds. With the help of this study, researchers can gather comprehensive data on studies regarding the recycling of waste bones, which will help them identify material recovery technologies and their applications in a single document. Furthermore, this work identifies areas for further research and development as well as areas for scaling-up, which will lead to reduced manufacturing costs and environmental impact. The idea behind this is to promote a sustainable environment and a circular economy concept in which waste bones are used as raw materials to produce new materials or for energy recovery.

Superior removal of humic acid from aqueous stream using novel calf bones charcoal nanoadsorbent in a reversible process

While the potable water disinfection regimen has significantly reduced waterborne diseases, development of disinfection byproducts (DBP) during this process has brought a global threat to the environment and human health. The most notorious water pollutant, humic acid (HA), transforms into carcinogenic byproducts during the disinfection process (chlorination) of water treatment. HA removal methods are neither economic nor widely available. This study addresses the most urgent global issue of HA removal by developing an innovative and self-regenerative process based on a low-cost and self-regenerative calf bone char (CBC) that removed 92.1-100% of HA. CBC-based HA removal has not been described yet. The developed CBC, as a super adsorbent of HA, was initially characterized by a scanning electron microscope. Various parameters of adsorption/desorption and self-regeneration of CBC adsorbent were experimentally determined. Results show that prepared CBC with a 112 m²/g surface area exhibited adsorption of 38.08 mg/g (HA = 20 mg/L, pH = 4.0) which is several folds higher than the typical amount of HA present in water. The 30 m reaction time was enough to remove HA which is the shorter HA time in comparison to other similar studies. The increase of HA from 0.5 to 5 g/L, raises % HA removal (36.7-99.8%) while a pH decrease (10-4) increases adsorption (12.3-98.3%). The adsorption data fitted well with the pseudo-second-order model and the Langmuir isotherm which demonstrate that adsorption takes place by a monolayer formation. Thermodynamic constants supported the endothermic, spontaneous and reversible nature of adsorption which can attain 100% HA removal. 100% regeneration of exhausted CBC by NaOH further supports the sustainability of the process. CBC as a new adsorbent material thus provides an economical and sustainable water pre-treatment procedure. The present study provides technical guidance for building a cost-effective and scalable process capable of providing clean water.

Removal of toluene and SO2 by hierarchical porous carbons: a study on adsorption selectivity and mechanism

The coal combustion produces a large amount of pollutants such as organic compounds pollutants (such as VOCs, SVOCs) and conventional pollutants (such as SO₂, NOx) which need to be controlled in coal-fired plants. Currently, there have been mature emission control technologies for conventional pollutants in coal-combustion flue gas. The complicated conditions of flue gas will have great effects on the property of VOCs adsorbents. Thus, high-quality adsorbents with great adsorption properties and selectivity of VOCs are urgently needed. In this work, a biomass-derived hierarchical porous carbon (HPC-A) with high adsorption capacity (585 mg/g) and great selectivity of toluene was proposed. Analyses through the competitive adsorption tests between toluene and SO₂ indicated that the pore size distributions of adsorbents dominate the adsorption capacity and selectivity. The ultramicropores (< 0.7 nm) determine the SO₂ adsorption capacity and promote the SO₂ adsorption selectivity, while the micropores of 0.7 ~ 2 nm and mesopores are beneficial for toluene adsorption. Intriguingly, the SO₂ molecules can promote the toluene adsorption kinetics on hierarchical porous carbons through occupying ultramicropores when competitive adsorption. Besides, we indicated the mechanism of adsorption capacity, selectivity, and kinetics of toluene and SO₂, and great reusability of HPC-A was found through toluene cyclic adsorption tests. The HPC-A could be a potential adsorbent for VOCs removal from coal-combustion flue gas.

Sago cycas-based hierarchical-structured porous carbon for adsorption of acetone vapour: preparation, characterization and performance

The porous structure and oxygen-containing functional groups of carbon materials play important roles in the adsorption of volatile organic compounds (VOCs). In this study, hierarchical-structured porous carbons (HSPCs) with a large specific surface area and abundant oxygen-containing functional groups were prepared from sago cycas without a template or post-processing for acetone (one of the most common VOCs) adsorption. The micropore volume (0.41-1.15 cm³ g^-1) and oxygen-containing functional groups (0.3-1.92 mmol g^-1) of HSPCs were manipulated by adjusting the activation temperature. Static adsorption data showed that the HSPC activated at 600 °C (HSPC-600) was superior for acetone adsorption, and a maximum adsorption capacity of 3.75 mmol g^-1 was achieved at 25 °C and 0.1 kPa. Breakthrough curves and cyclic adsorption-desorption tests demonstrated the dynamic adsorption capacity and regeneration performance of HSPC-600 were excellent as well. The adsorption isotherms were well described by Langmuir and Langmuir-Freundlich models, indicating the adsorption of acetone on HSPCs is a monolayer adsorption process. Due to electrostatic interaction, hydrogen bond and van der Waals forces between acetone molecules and oxygen-containing functional groups, the adsorption capacity of HSPCs for acetone was significantly improved at low relative pressure. This study may provide a peculiar insight into the development of high-performance acetone adsorbent.

Hierarchical porous structure formation mechanism in food waste component derived N-doped biochar: Application in VOCs removal

Nitrogen-doped (N-doped) hierarchical porous carbon was widely utilized as an efficient volatile organic compounds (VOCs) adsorbent. In this work, a series of N-doped hierarchical porous carbons were successfully prepared from the direct pyrolysis process of three food waste components. The porous biochar that derived from bone showed a high specific surface area (1405.06 m²/g) and sizable total pore volume (0.97 cm³/g). The developed hierarchical porous structure was fabricated by the combined effect of self-activation (Carbon dioxide (CO₂) and water vapor (H₂O)) and self-template. The emission characteristics of activation gas analyzed by Thermogravimetric-Fourier transform infrared spectrometer (TG-FTIR) and the transformation of ash composition in the biochar help to illustrate the pore-forming mechanism. Calcium oxide (CaO) and hydroxylapatite were confirmed as the major templates for mesopores, while the decomposition processes of calcium carbonate (CaCO₃) and hydroxylapatite provided a large amount of activation gas (CO₂ and H₂O) to form micropores. The materials also obtained abundant N-containing surface functional groups (up to 7.84 atomic%) from pyrolysis of protein and chitin. Finally, the porous biochar showed excellent performance for VOCs adsorption with a promising uptake of 288 mg/g for toluene and a high adsorption rate of 0.189 min^-1. Aplenty of mesopores distributed in the materials effectively improved the mass transfer behaviors, the adsorption rate got a noticeable improvement (from 0.118 min^-1 to 0.189 min^-1) benefited from mesopores. Reusable potentials of the hierarchical porous carbons were also satisfying. After four thermal regeneration cycles, the materials still occupied 84.8%-87.4% of the original adsorption capacities.

How to predict emissions of volatile organic compounds from solid building materials? A critical review on mass transfer models

Volatile organic compounds (VOCs) emitting from solid building materials can cause adverse human health and environmental climate effects. It's more cost effective and powerful for mass-transfer emission models to describe the emission characteristic of VOCs than emission chamber studies. In this review, the existing main physical mechanism-based models for predicting VOCs emissions from dry solid building materials have been discussed, as well as their differences and similarities. Ignoring internal diffusion and porosity of solid materials, single-phase model is generally quite safe for use in actual condition. Conversely, porous media model is good for understanding VOC-transfer principles in porous materials. Additionally, the porous media model and the single-phase model can be transformed mutually because their model parameters are correlative. The availability of emission models is largely determined by the reliable and useful model parameters. Therefore, substantial technologies and novel methods have been developed for parameter estimation, which have also been reviewed in this paper. How to readily and rapidly obtain model parameters is a future development direction. In addition, applying emission models to predict and control VOCs emission from other solid waste materials is another future research prospect.

Preparation and characterization of magnetic modified bone charcoal for removing Cu2+ ions from industrial and mining wastewater

Heavy metal water pollution is an urgent global problem to be addressed. Copper ions are common toxic heavy metal pollutants in wastewater. In order to remove the excessive copper ions in wastewater, in this study, chicken bone charcoal was modified by sodium dodecyl sulfonate and combined with magnetic nanoparticles prepared with ferric chloride hexahydrate and ferrous sulfate heptahydrate to produce a high efficiency adsorbent. The characterization of the magnetically modified bone charcoal was analyzed by scanning electron microscopy, surface and porosity analyses, FTIR and thermogravimetric analysis. The optimal adsorption conditions of magnetically modified bone charcoal for Cu²⁺ were obtained through batch experiments. The highest removal rate and adsorption capacity of Cu²⁺ was 99.98% and 15.057 mg/g, respectively, when the pH was 3.0, adsorbent dosage was 0.2 g, initial concentration of the Cu²⁺ solution was 50 mg/L, and temperature was 25 °C. The adsorption process fitted well with the Langmuir isotherm and the pseudo-second-order kinetic model. The regeneration experiment indicated that M-SDS-BC-500 maintained a high removal rate after five repetitions. The results suggest that the adsorbent has wide application prospects.

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.

Preparation of sludge-based activated carbon for adsorption of dimethyl sulfide and dimethyl disulfide during sludge aerobic composting

Emission of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) during sludge aerobic composting has limited the use and development of this economical sludge treatment process. In this study, cheap and easily available sludge was used as raw material for the preparation of adsorbents to eliminate DMS and DMDS. A series of sludge-based activated carbons (SACs) were prepared by acid or base activation, and coconut shell mix was also assessed. The results revealed that SAC preparation by KOH activation without coconut shell mix could significantly enhance the surface area and pore volume of SAC, and showed the maximum adsorption capacity for DMS (53.45 mg g^-1) and DMDS (151.28 mg g^-1). In addition, SAC had a good adsorption effect on a mixture of DMS and DMDS. The SAC adsorbents could efficiently adsorb DMS and DMDS after four cycles of regeneration. Thermodynamic and kinetic analyses demonstrated that adsorption between the SAC and DMS/DMDS was via physical adsorption. The SAC developed in this study utilized waste in a useful way that could significantly reduce the cost of adsorbents and use them for odor elimination during sludge aerobic composting.

Synthesis of N-doped hierarchical porous carbon with excellent toluene adsorption properties and its activation mechanism

Typical organic pollutants from coal-combustion flue gas such as volatile organic compounds (VOCs) need to be effectively controlled. This work synthesized a series of nitrogen-doped hierarchical porous carbons (NHPCs) by one-step activation with various proportions of cellulose, (NH₄)₂C₂O₄ and KHCO₃/NaHCO₃. The NHPCs have a high specific surface area and pore volume up to 2816 m²/g and 1.413 cm³/g as well as a hierarchical porous structure with micro-meso-macropores distribution. The dynamic adsorption tests of toluene at 600 ppm showed that NHPCs have a high adsorption capacity up to 585 mg/g (NHPC(K)131), this was about 3 times more than that of AC (208 mg/g), and is a better absorbent compared to many other carbon adsorbents. The porous characteristics and toluene adsorption properties of NHPCs improved along with the fluctuation of the proportions of raw materials and active agents. The micropore size of the material is the main factor that affecting the toluene adsorption capacity. The analysis of toluene dynamic adsorption breakthrough curves revealed that NHPCs had great toluene adsorption kinetics with high adsorption rate constants and short mass transfer zone. The excellent toluene adsorption kinetics of NHPCs can be attributed to the hierarchical porous structure. The abundant 2-10 nm mesopores and macropores of NHPCs act as mass transfer channels for toluene molecules. The XPS analysis showed that the NHPCs have nitrogen doping up to 6.71% (NHPC(Na)161) and they effectively promote toluene adsorption. The nitrogen doping mechanism can be attributed to the reactions between cellulose pyrolysis substances and NH₃ which decomposed from (NH₄)₂C₂O₄. Moreover, the pore forming reactivity of KHCO₃ is better than that of NaHCO₃ in the NHPCs activation process.

Facile synthesis of tailored mesopore-enriched hierarchical porous carbon from food waste for rapid removal of aromatic VOCs

Due to the large amount, environmental impact, and complex properties of accumulated food waste, its disposal and valorization has become a growing global concern and challenges. In this study, a series of mesopore-enriched hierarchical porous carbons were synthesized from a mixture of two food waste components (peptone and bone). The prepared materials were employed for the rapid adsorption of aromatic volatile organic compounds (VOCs). The pore structures, morphology and surface chemistry of the food waste-based microporous activated carbon (PCs) and mesopore-enriched hierarchical porous carbons (PC/BCs) were characterized and then compared. PC/BCs presented larger pore volume (2.45 cm³/g vs. 1.25 cm³/g) than the PCs because of their activation and the template effect of the bone, allowing them to exhibit satisfactory adsorption capacities (139.5 mg/g for benzene and 440.7 mg/g for toluene) and adsorption rate (0.285 min^-1 for benzene and 0.236 min^-1 for toluene) for aromatic VOCs. In addition, a strong linear relationship (R² = 0.957) was also established between the adsorption rate k and total pore volume, highlighting the role of mesopores in PC/BCs, which contributed 60% to the total pore volume, during the rapid capture of VOCs. Further, PC/BCs also showed excellent thermal regeneration performance for more than four runs. The results of this study provide a feasible approach to fabricating mesopore-enriched hierarchical porous carbon from food waste, which could enable the rapid removal of VOCs.

SERS Approach to Probe the Adsorption Process of Trace Volatile Benzaldehyde on Layered Double Hydroxide Material

The study of the physicochemical process of volatile organic compound (VOC) adsorption on porous materials is significant for design and screening of adsorbent materials and treatment of VOCs. Traditional measurement methods for studying the adsorption process require lots of adsorbates and adsorbents and are time-consuming. We proposed a facile strategy to study the adsorption process of trace gaseous aldehydes on layered double hydroxide (LDH) using surface-enhanced Raman spectroscopy (SERS). We prepared a composite of Ag nanocubes@hollow Co-Ni LDH (AgNCs@Co-Ni LDH) with a strong adsorption capability and high SERS sensitivity. The adsorption properties of LDH for benzaldehyde in terms of general kinetics and isotherms were investigated. The kinetic adsorption process could be fitted better by the pseudo-first-order kinetics with a higher correlation coefficient than by the pseudo-second-order model, and the adsorption rate of 0.0308 min^-1 was obtained from the fitting curve. The isotherm adsorption fits the Langmuir isotherm model, and its adsorption constant is 6.25 × 10⁶ L/mol. Taking advantage of the excellent adsorptive performance and SERS activity, the AgNCs@Co-Ni LDH composite can be used as an effective SERS probe to detect gaseous aldehydes, and it shows a linear dynamic range (5-100 ppb) with a limit of detection reaching 1.83 ppb for benzaldehyde, better than that achieved by previous studies. Therefore, this work has not only established a new measurement method for probing the adsorption process with extremely low consumption of both adsorbates and adsorbents, but also may lay the groundwork for the construction of rapid and ultra-sensitive SERS sensors for probing VOCs in the future.

Energy-Saving and Sustainable Separation of Bioalcohols by Adsorption on Bone Char

The separation of ethanol, propanol, and butanol from aqueous solutions was studied using adsorption on bone char. Adsorption kinetics and thermodynamic parameters of this separation method were studied at different conditions of pH and temperature. Results showed that the maximum adsorption capacities of these bioalcohols were obtained at pH 6 and 20°C. An exothermic separation was identified, which can be mainly associated to hydrophobic interactions between bone char surface and bioalcohols. Binary adsorption studies were also performed using mixtures of these bioalcohols. An antagonistic adsorption was observed for all bioalcohols where the ethanol and propanol separation was significantly affected by butanol. A model based on an artificial neural network was proposed to correlate both single and binary adsorption isotherms of these bioalcohols with bone char. It was concluded that the bone char could be an interesting adsorbent for the sustainable separation and recovery of bioalcohols from fermentation broths, which are actually considered emerging liquid biofuels and relevant industrial chemicals.