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•Adsorption process of heavy metals on the biochars was modeled by machine learning.•RF model showed better predicting performance (R2 = 0.973) than ANN model.•The biochar ...characteristics (54%) was the most significant for adsorption efficiency.•CEC and pHH2O of biochars have large contribution to adsorbing heavy metals.•Models developed by RF have more generalization ability than ANN model.
The adsorption of six heavy metals (lead, cadmium, nickel, arsenic, copper, and zinc) on 44 biochars were modeled using artificial neural network (ANN) and random forest (RF) based on 353 dataset of adsorption experiments from literatures. The regression models were trained and optimized to predict the adsorption capacity according to biochar characteristics, metal sources, environmental conditions (e.g. temperature and pH), and the initial concentration ratio of metals to biochars. The RF model showed better accuracy and predictive performance for adsorption efficiency (R2 = 0.973) than ANN model (R2 = 0.948). The biochar characteristics were most significant for adsorption efficiency, in which the contribution of cation exchange capacity (CEC) and pHH2O of biochars accounted for 66% in the biochar characteristics. However, surface area of the biochars provided only 2% of adsorption efficiency. Meanwhile, the models developed by RF had better generalization ability than ANN model. The accurate predicted ability of developed models could significantly reduce experiment workload such as predicting the removal efficiency of biochars for target metal according to biochar characteristics, so as to select more efficient biochar without increasing experimental times. The relative importance of variables could provide a right direction for better treatments of heavy metals in the real water and wastewater.
Selective removal of arsenic (As) is the key challenge for any of As removal mechanisms as this not only increases the efficiency of removal of the main As species (neutral As(III) and As(V) ...hydroxyl-anions) but also allows for a significant reduction of waste as it does not co-remove other solutes. Selective removal has a number of benefits: it increases the capacity and lifetime of units while lowering the cost of the process. Therefore, a sustainable selective mitigation method should be considered concerning the economic resources available, the ability of infrastructure to sustain water treatment, and the options for reuse and/or safe disposal of treatment residuals. Several methods of selective As removal have been developed, such as precipitation, adsorption and modified iron and ligand exchange. The biggest challenge in selective removal of As is the presence of phosphate in water which is chemically comparable with As(V). There are two types of mechanisms involved with As removal: Coulombic or ion exchange; and Lewis acid-base interaction. Solution pH is one of the major controlling factors limiting removal efficiency since most of the above-mentioned methods depend on complexation through electrostatic effects. The different features of two different As species make the selective removal process more difficult, especially under natural conditions. Most of the selective As removal methods involve hydrated Fe(III) oxides through Lewis acid-base interaction. Microbiological methods have been studied recently for selective removal of As, and although there have been only a small number of studies, the method shows remarkable results and indicates positive prospects for the future.
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•Selective arsenic (As) removal increase removal units' lifetime, decrease waste, costs.•Phosphate is the principal competitor for all selective As removal approaches.•Simultaneous selective removal of As(V) and As(III) requires composite approaches.•Lewis acid-base interaction & ion-exchange are the major mechanisms involved.•Microbial methods have potential in selective As removal as an economical method.
Volatile organic compounds (VOCs) are harmful for human and surrounding ecosystem, and a great number of VOC abatement technologies have been developed during the past few decades. However, the ...single method has some problems such as high energy consumption, unfriendly environment, and low removal efficiency. Recently, the integration of adsorption and photocatalytic degradation of VOCs is considered as a promising one. Carbon material, with large surface area, high adsorption capacity, and fast electron transfer ability, is widely used in integrated adsorptive-photocatalytic removal of VOCs. It is thus crucial to digest and summarize recent research advances in carbon-based nanocomposites as the adsorbent-photocatalyst for VOC removal. To satisfy this need, this work provides a critical review of the related literature with focuses on: (1) the advantages and disadvantages of various carbon-based nanocomposites for the applications of VOC adsorption and photocatalytic degradation; (2) models and mechanisms of adsorptive-photocatalytic removal of VOCs according to the material properties; and (3) major factors controlling adsorption-photocatalysis processes of VOCs. The review is aimed to establish the “structure-property-application” relationships for the development of innovative carbon-supported nanocomposites and to promote future research on the integrated adsorptive and photocatalytic removal of VOCs.
•The advantages and disadvantages of carbon-supported hybrids were discussed.•Adsorption and photocatalytic models of VOC removal were reviewed.•The reaction processes and intermediates were proposed.•Major factors controlling adsorptive-photocatalytic reactions were discussed.
•Aggregation and passivation of nZVI can be alleviated by surfactants and doping methods.•BC hinders corrosion and improves the dispersion and electron transfer of nZVI.•Properties of nZVI depend on ...those of the BC, feedstock and pyrogenic temperature.•BC enhances electron transfer from nZVI to the contaminants due to the presence of quinone and graphene moieties.•nZVI/BC shows strong ability to remove HMs, nitrates, and organic contaminants in soil and water.
The promising characteristics of nanoscale zero-valent iron (nZVI) have not been fully exploited owing to intrinsic limitations. Carbon-enriched biochar (BC) has been widely used to overcome the limitations of nZVI and improve its reaction with environmental pollutants. This work reviews the preparation of nZVI/BC nanocomposites; the effects of BC as a supporting matrix on the nZVI crystallite size, dispersion, and oxidation and electron transfer capacity; and its interaction mechanisms with contaminants. The literature review suggests that the properties and preparation conditions of BC (e.g., pore structure, functional groups, feedstock composition, and pyrogenic temperature) play important roles in the manipulation of nZVI properties. This review discusses the interactions of nZVI/BC composites with heavy metals, nitrates, and organic compounds in soil and water. Overall, BC contributes to the removal of contaminants because it can attenuate contaminants on the surface of nZVI/BC; it also enhances electron transfer from nZVI to target contaminants owing to its good electrical conductivity and improves the crystallite size and dispersion of nZVI. This review is intended to provide insights into methods of optimizing nZVI/BC synthesis and maximizing the efficiency of nZVI in environmental cleanup.
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•Gamma-valerolactone is a precursor for valuable chemicals and potential fuel additive.•Non-noble metals can be used in catalytic transfer hydrogenation (CTH) to produce ...GVL.•Dispersion of metal particles on catalysts influences hydrogenation efficiency.•Lewis acid and base sites are needed for obtaining high GVL yield and selectivity.•Metal leaching from catalysts is significant in aqueous conditions.
The distinct physicochemical properties and renewable origin of gamma-valerolactone (GVL) have provided opportunities for diversifying its applications, particularly as a green solvent, excellent fuel additive, and precursor to valuable chemicals. Among the related publications found in the SCOPUS database (≈172 in the last 10 years), we focused our effort to review the conversion of levulinic acid (LA) to GVL over non-noble metal catalysts and the corresponding mechanisms (≈30 publications) as well as the applications of GVL as a solvent, fuel additive, and platform chemical (≈30 publications) mostly in the last five years (some preceding publications have also been included due to their relevance and importance in the field). The use of non-noble metals (e.g., Cu and Zr) presents a greener route of GVL synthesis than the conventional practice employing noble metals (e.g., Pd and Ru), in view of their higher abundance and milder reaction conditions needed (e.g., low pressure and temperature without H2 involved). The significance of the catalyst characteristics in promoting catalytic transfer hydrogenation of LA to GVL is critically discussed. Structural features and acid-base properties are found to influence the activity and selectivity of catalysts. Furthermore, metal leaching in the presence of water in catalytic systems is an important issue, resulting in catalyst deactivation. Various endeavors for developing catalysts using well-dispersed metal particles along with a combination of Lewis acid and base sites are suggested for efficiently synthesizing GVL from LA.
This review focuses on contaminant removal from water using hydrogel-based materials. It highlights the recent results achieved, unresolved problems, and possible developments. Polymer and graphene ...hydrogels are promising new materials for removing inorganic (e.g., metals and metalloids) and organic (e.g., dyes) trace contaminants from water. They can be prepared as composites with practically any desired conventional or innovative adsorbent, to enhance the removal efficiency. Obtaining a three-dimensional highly effective network is one of the significant features of hydrogels, which confer specific characteristics on them. There are number of benefits of using hydrogels: easy separation and handling, the facility for large-scale application, and the ability to regenerate and reuse the hydrogels. At present, the experiments based on hydrogels for water purification are mostly limited to the laboratory scale and further research needed to move toward large-scale industrial applications. Moreover, the present studies are currently limited to a few types of contaminants, so that further experiments needed for removal of more contaminant types and mixtures of contaminants, considering that in practical situations. All these features are described and discussed in this review, which, to the best of our knowledge, is the first comprehensive review on hydrogel applications for contaminant removal from water.
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•Aromatics and carbon materials can be produced from lignin valorization.•Heterogeneous or electrocatalytic hydrogenolysis is promising for aromatics production.•Lignin ...biochar/hydrochar can serve as new carbon materials for emerging applications.•Efficient lignin depolymerisation and degradation is the key to scaled-up valorization.
Lignin is an abundant biomass resource in aromatic structure with a low price in market, which can serve as renewable precursors of value-added products. However, valorization rate of annually produced lignin is less than 2%, suggesting the need for technological advancement to capitalize lignin as a versatile feedstock. In recent years, efficient utilization of lignin has attracted wide attention. This paper summarizes the research advances in the utilization of lignin resources (mainly in the last three years), with a particular emphasis on two major approaches of lignin utilization: catalytic degradation into aromatics and thermochemical treatment for carbon material production. Hydrogenolysis, direct pyrolysis, hydrothermal liquefaction, and hydrothermal carbonization of lignin are discussed in detail. Based on this critical review, future research directions and development prospects are proposed for sustainable and cost-effective lignin valorization.
Mesoporous silica nanoparticles (MSNs), one of the important porous materials, have garnered interest owing to their highly attractive physicochemical features and advantageous morphological ...attributes. They are of particular importance for use in diverse fields including, but not limited to, adsorption, catalysis, and medicine. Despite their intrinsic stable siliceous frameworks, excellent mechanical strength, and optimal morphological attributes, pristine MSNs suffer from poor drug loading efficiency, as well as compatibility and degradability issues for therapeutic, diagnostic, and tissue engineering purposes. Collectively, the desirable and beneficial properties of MSNs have been harnessed by modifying the surface of the siliceous frameworks through incorporating supramolecular assemblies and various metal species, and through incorporating supramolecular assemblies and various metal species and their conjugates. Substantial advancements of these innovative colloidal inorganic nanocontainers drive researchers in promoting them toward innovative applications like stimuli (light/ultrasound/magnetic)‐responsive delivery‐associated therapies with exceptional performance in vivo. Here, a brief overview of the fabrication of siliceous frameworks, along with discussions on the significant advances in engineering of MSNs, is provided. The scope of the advancement in terms of structural and physicochemical attributes and their effects on biomedical applications with a particular focus on recent studies is emphasized. Finally, interesting perspectives are recapitulated, along with the scope toward clinical translation.
Mesoporous silica nanoparticles (MSNs) have garnered enormous interest owing to their highly advantageous physicochemical and morphological attributes. Collectively, progression has been made by modifying the surface of the siliceous frameworks through incorporating diverse supramolecular assemblies. An overview of the fabrication of MSNs and discussions on significant advances in engineering of MSNs, along with their scope toward clinical translation, is provided.
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This review provides a brief overview of the potential applications of hydrochar and its derivatives. It first summarized the key processes of hydrothermal carbonization (HTC) of ...biomass and basic properties of the resulting hydrochar. Most of the efforts of this review is then on reviewing the potential applications of hydrochar in various fields including environment, energy, adsorbent and medical applications. It also discusses different modification and activation methods to produce hydrochar-based engineered carbon materials for enhanced performances in those applications, particularly with respect to their application as low-cost adsorbents for the removal of heavy metals, organics, phosphate and pathogens.
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•Corn stalk biochar is engineered with crystalline Zn/Al, Mg/Al, and Ni/Fe LDH flakes.•BC-M-LDH composites combine advantages of porous biochar with LDH minerals.•Fast kinetics and ...high adsorption capacity of phosphorus are demonstrated.•Interlayer ion exchange and surface complexation are involved in phosphorus recovery.
Highly efficient and cost-effective adsorbents for phosphate (P) recovery are the key to control eutrophication and recover phosphorus from waste streams to enhance food production. This study assembled corn stalk-derived biochar (BC) with various forms of layered double hydroxides (LDHs) (B-M-LDH) through simultaneous pyrolysis of waste biomass and metal (i.e., Zn/Al, Mg/Al, and Ni/Fe) hydroxide precipitates. Batch sorption experiments evaluated the kinetics and isotherms of phosphate adsorption as well as the influence of pH value and co-existing anions. Morphological characterization showed that crystalline LDH flakes were impregnated within the framework of fabricated B-M-LDH composites. Superior P adsorption capacity (152.1 mg (P) g−1) and fast Elovich kinetics (5925 mg g−1 h−1) could be achieved by the B-Zn/Al-LDH composite at pH 5. The P adsorption onto BC-LDHs was pH dependent and subjected to adverse influence of co-existing anions. Interlayer anion exchange and surface complexation were probably the predominant adsorption mechanisms at the studied phosphate concentration. Therefore, BC can be functionalized as mineral composites for enhancing P recovery and wastewater treatment.
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