Recovery of non-metallic useable materials from e-waste.

Tremendous amounts of electric and electronic wastes (e-waste) are generated daily, and their indiscriminate disposal may cause serious environmental pollution. The recovery of non-metallic materials from e-waste is a strategy to not only reduce the volume of e-waste but also avoid pollutant emissions produced by indiscriminate disposal of e-waste. Pyrolysis, sub/supercritical water treatment, chemical dissolution, and physical treatment (e.g., ball milling, flotation, and electrostatic separation) are available methods to recover useable non-metallic materials (e.g., resins, fibers, and various kinds of polymers) from e-waste. The e-waste-derived materials can be used to manufacture a large variety of industrial and consumer products. In this regard, this work attempts to compile relevant knowledge on the technologies that derive utilizable materials from different classes of e-waste. Moreover, this work highlights the potential of the e-waste-derived materials for various applications. Current challenges and perspectives on e-waste upcycling to useable materials are also discussed.

Recent advances in liquid fuel production from plastic waste via pyrolysis: Emphasis on polyolefins and polystyrene.

The management of plastic waste (PW) has become an indispensable worldwide issue because of the enhanced accumulation and environmental impacts of these waste materials. Thermo-catalytic pyrolysis has been proposed as an emerging technology for the valorization of PW into value-added liquid fuels. This review provides a comprehensive investigation of the latest advances in thermo-catalytic pyrolysis of PW for liquid fuel generation, by emphasizing polyethylene, polypropylene, and polystyrene. To this end, the current strategies of PW management are summarized. The various parameters affecting the thermal pyrolysis of PW (e.g., temperature, residence time, heating rate, pyrolysis medium, and plastic type) are discussed, highlighting their significant influence on feed reactivity, product yield, and carbon number distribution of the pyrolysis process. Optimizing these parameters in the pyrolysis process can ensure highly efficient energy recovery from PW. In comparison with non-catalytic PW pyrolysis, catalytic pyrolysis of PW is considered by discussing mechanisms, reaction pathways, and the performance of various catalysts. It is established that the introduction of either acid or base catalysts shifts PW pyrolysis from the conventional free radical mechanism towards the carbonium ion mechanism, altering its kinetics and pathways. This review also provides an overview of PW pyrolysis practicality for scaling up by describing techno-economic challenges and opportunities, environmental considerations, and presenting future outlooks in this field. Overall, via investigation of the recent research findings, this paper offers valuable insights into the potential of thermo-catalytic pyrolysis as an emerging strategy for PW management and the production of liquid fuels, while also highlighting avenues for further exploration and development.

Enhanced mono-aromatics production by the CH4-assisted pyrolysis of microalgae using Zn-based HZSM-5 catalysts.

This study presents the catalytic pyrolysis of microalgae, Chlorella vulgaris (C. vulgaris), using pure CH4 and H2-rich gas evolved from CH4 decomposition on three different HZSM-5 catalysts loaded with Zn, Ga, and Pt, aimed specifically at producing high-value mono-aromatics such as benzene, toluene, ethylbenzene, and xylene (BTEX). In comparison with that for the typical inert N2 environment, a pure CH4 environment increased the bio-oil yield from 32.4 wt% to 37.4 wt% probably due to hydrogen and methyl radical insertion in the bio-oil components. Furthermore, the addition of bimetals further increased bio-oil yield. For example, ZnPtHZ led to a bio-oil yield of 47.7 wt% in pure CH4. ZnGaHZ resulted in the maximum BTEX yield (6.68 wt%), which could be explained by CH4 activation, co-aromatization, and hydrodeoxygenation. The BTEX yield could be further increased to 7.62 wt% when pyrolysis was conducted in H2-rich gas evolved from CH4 decomposition over ZnGaHZ, as rates of aromatization and hydrodeoxygenation were relatively high under this condition. This study experimentally validated that the combination of ZnGaHZ and CH4 decomposition synergistically increases BTEX production using C. vulgaris.

Sustainable ethylene production: Recovery from plastic waste via thermochemical processes.

The concept of monomer recovery from plastic waste has recently gained broad interest in industry as a powerful strategy to reduce the environmental impacts of chemical production and plastic waste pollution. Herein, we focus on the ethylene recovery from plastic waste via thermochemical pathways, such as pyrolysis, gasification, and steam cracking of pyrolysis oil derived from plastic waste. Ethylene recovery performance of different thermochemical conversion processes is evaluated and compared with respect to plastic waste types, process types, ethylene recovery yields, and process operating conditions. Based on the analysis of available data in earlier literature, future research is recommended to further enhance the viability of the thermochemical ethylene recovery technologies. This review is expected to offer a meaningful guideline on developing efficient platforms for the value-added monomer recovery from plastic waste through thermochemical conversion routes. It is also hoped that this review serves as a preliminary step to encourage the widespread adoption of thermochemical conversion-based ethylene recovery from plastic waste by industries.

Schiff base-functionalized metal-organic frameworks as an efficient adsorbent for the decontamination of heavy metal ions in water.

Adsorptive removal of heavy metal ions from water is an energy- and cost-effective water decontamination technology. Schiff base functionalities can be incorporated into the pore cages of metal-organic frameworks (MOFs) via direct synthesis, post-synthetic modification, and composite formation. Such incorporation can efficiently enhance the interactions between the MOF adsorbent and target heavy metal ions to promote the selective adsorption of the latter. Accordingly, Schiff base-functionalized MOFs have great potential to selectively remove a particular metal ion from the aqueous solutions in the presence of coexisting (interfering) metal ions through the binding sites within their pore cages. Schiff base-functionalized MOFs can bind divalent metal ions (e.g., Pb(II), Co(II), Cu(II), Cd (II), and Hg (II)) more strongly than trivalent metal ions (e.g., Cr(III)). The adsorption capacity range of Schiff base-functionalized MOFs for divalent ions is thus much more broad (22.4-713 mg g-1) than that of trivalent metal ions (118-127 mg g-1). To evaluate the adsorption performance between different adsorbents, the two parameters (i.e., adsorption capacity and partition coefficient (PC)) are derived and used for comparison. Further, the possible interactions between the Schiff base sites and the target heavy metal ions are discussed to help understand the associated removal mechanisms. This review delivers actionable knowledge for developing Schiff-base functionalized MOFs toward the adsorptive removal of heavy metal ions in water in line with their performance evaluation and associated removal mechanisms. Finally, this review highlights the challenges and forthcoming research and development needs of Schiff base-functionalized MOFs for diverse fields of operations.

Strategic use of crop residue biochars for removal of hazardous compounds in wastewater.

Crop residues are affordable lignocellulosic waste in the world, and a large portion of the waste has been burned, releasing toxic pollutants into the environment. Since the crop residue is a carbon and ingredient rich material, it can be strategically used as a sorptive material for (in)organic pollutants in the wastewater after thermo-chemical valorization (i.e., biochar production). In this review, applications of crop residue biochars to adsorption of non-degradable synthetic dyes, antibiotics, herbicides, and inorganic heavy metals in wastewater were discussed. Properties (porosity, functional groups, heteroatom, and metal(oxide)s, etc.) and adsorption capacity relationships were comprehensively reviewed. The current challenges of crop residue biochars and guidelines for development of efficient adsorbents were also provided. In the last part, the future research directions for practical applications of the crop residue biochars in wastewater treatment plants have been suggested.

Hollow-Structured N-doped carbon-embedded CoFe NanoAlloy for boosting activation of Monopersulfate: Engineered interface and heteroatom Doping-Induced enhancements.

While transition metals are useful for activating monopersulfate (MPS) to degrade contaminants, bimetallic alloys exhibit stronger catalytic activities owing to several favorable effects. Therefore, even though Co is an efficient metal for MPS activation, CoFe alloys are even more promising heterogeneous catalysts for MPS activation. Immobilization/embedment of CoFe alloy nanoparticles (NPs) onto hetero-atom-doped carbon matrices appears as a practical strategy for evenly dispersing CoFe NPs and enhancing catalytic activities via interfacial synergies between CoFe and carbon. Herein, N-doped carbon-embedded CoFe alloy (NCCF) is fabricated here to exhibit a unique hollow-engineered nanostructure and the composition of CoFe alloy by using Co-ZIF as a precursor after the facile etching and Fe doping. The Fe dopant embeds CoFe alloy NPs into the hollow-structured N-doped carbon substrate, enabling NCCF to possess the higher mesoscale porosity, active N species as well as more superior electrochemical properties than its analogue without Fe dopants, carbon matrix-supported cobalt (NCCo). Thus, NCCF exhibits a considerably larger activity than NCCo and the benchmark catalyst, Co3O4 NP, for MPS activation to degrade an environmental hormone, dihydroxydiphenyl ketone (DHPK). Besides, NCCF + MPS shows an even lower activation energy for DHPK degradation than literatures, and retains its high efficiency for eliminating DHPK in different water media. DHPK degradation pathway and ecotoxicity assessment are unraveled based on the insights from the computational chemistry, demonstrating that DHPK degradation by NCCF + MPS did not result in the formation of toxic and highly toxic by-products. These features make NCCF a promising heterogeneous catalyst for MPS activation to degrade DHPK.

Abatement of odor emissions from wastewater treatment plants using biochar.

Odor is a critical environmental problem that negatively affects people's quality of life. Wastewater treatment plants (WWTPs) often emit various odorous compounds, such as ammonia, sulfur dioxide, and organosulfur. Abatement of odor emissions from WWTPs using biochar may contribute to achieving carbon neutrality due to the carbon negative nature, CO2 sorption, and negative priming effects of biochar. Biochar has a high specific surface area and microporous structure with appropriate activation, which is suitable for sorption purposes. Various research directions have been proposed to determine the biochar removal efficiency for different odorants released from WWTPs. According to the literature survey, the pre- and post-treatments (e.g., thermal treatment, chemical treatment, and metal impregnation) of biochar could enhance the removal capacity for the odorants emitted from WWTPs at comparable conditions, compared to unmodified biochar. The feedstock and production condition (particularly, pyrolysis temperature) of a biochar and initial concentration of an odorant markedly affect the biochar's odorant removal capacity and efficiency. Moreover, different adsorption systems for the removal of odorants emitted from WWTPs follow different adsorption models. Further research is required to establish the practical use of biochar for the mitigation of odors released from WWTPs.

Reduction of odor-causing compounds in wastewater using biochar: A review.

Wastewater contains chemical compounds that cause malodors, such as ammonium cation, dimethyl sulfide, and volatile organic compounds. Biochar-based reduction in the odorants has been proposed as an effective approach along with maintaining environmental neutrality as biochar is a sustainable material made from biomass and biowaste. Biochar can have high specific surface area and microporous structure with proper activation, appropriate for sorption purposes. Recently, various research directions have been proposed to determine the removal efficiency of biochar for different odorants contained in wastewater. This article is aimed at providing the most updated review of biochar-based removal of odor-causing compounds in wastewater while highlighting the current advances. It was distinguished that the odorant removal performance of biochar is highly associated with the raw material and modification method of biochar, and the kind of odorants. Further research should be required for more practical use of biochar for the reduction of odorants in wastewater.

Cycling of phosphorus from wastewater to fertilizer using wood ash after energy production.

Quercus wood was used for thermal energy production, and wood bottom ash (WDBA) was used as a medium for water purification and soil fertilizer in accordance with the recently proposed food-water-energy nexus concept. The wood contained a gross calorific value of 14.83 MJ kg-1, and the gas generated during thermal energy production has the advantage of not requiring a desulfurization unit due to its low sulfur content. Wood-fired boilers emit less CO2 and SOX than coal boilers. The WDBA had a Ca content of 66.0%, and Ca existed in the forms of CaCO3 and Ca(OH)2. WDBA absorbed P by reacting with Ca in the form of Ca5(PO4)3OH. Kinetic and isotherm models revealed that the results of the experimental work were in good agreement with the pseudo-second-order and Langmuir models, respectively. The maximum P adsorption capacity of WDBA was 76.8 mg g-1, and 6.67 g L-1 of WDBA dose could completely remove P in water. The toxic units of WDBA tested using Daphnia magna were 6.1, and P adsorbed WDBA (P-WDBA) showed no toxicity. P-WDBA was used as an alternative P fertilizer for rice growth. P-WDBA application resulted in significantly greater rice growth in terms of all agronomic values compared to N and K treatments without P. This study proposed the utilization of WDBA, obtained from thermal energy production, to remove P from wastewater and replenish P in the soil for rice growth.

Effects of Ni/Al2O3 catalyst treatment condition on thermocatalytic conversion of spent disposable wipes.

Municipal solid waste (MSW) management is an essential municipal service. Proper waste treatment is an important part of the waste management. Thermocatalytic waste upcycling has recently gained great interest and attention as a method to extract value from waste, which potentially substitutes traditional waste treatment methods. This study aims at demonstrating the potential for thermocatalytic waste upcycling using spent disposable wipes as an MSW surrogate. Two different Ni/Al2O3 catalysts were prepared, treated under two different atmospheres (N2 and CO2). The catalyst treated in N2 (Ni/Al2O3-N2) exhibited a higher surface metallic Ni site than the catalyst treated in CO2 (Ni/Al2O3-CO2). The use of the Ni/Al2O3-N2 increased the yield of gas pyrolysate and decreased the yield of byproduct (e.g., wax), compared with no catalyst and the Ni/Al2O3-CO2. In particular, the Ni/Al2O3-N2 catalyst affected the generation of gaseous hydrogen (H2) by increasing the H2 yield by up to 102% in comparison with the other thermocatalytic systems. The highest H2 yield obtained with the Ni/Al2O3-N2 was attributed to the most surface metallic Ni sites. However, the Ni/Al2O3-N2 catalyst led to char having a lower higher heating value than the other catalysts due to its lowest carbon content. The results indicated that the reduction treatment environment for Ni/Al2O3 catalyst influences thermocatalytic conversion product yields of spent disposable wipes, including enhanced H2 production. Electronic Supplementary Material: Supplementary material is available in the online version of this article at 10.1007/s11814-023-1461-8.

Plastic-Waste-Derived Char as an Additive for Epoxy Composite.

Tremendous amounts of plastic waste are generated daily. The indiscriminate disposal of plastic waste can cause serious global environmental issues, such as leakages of microplastics into the ecosystem. Thus, it is necessary to find a more sustainable way to reduce the volume of plastic waste by converting it into usable materials. Pyrolysis provides a sustainable solution for the production of carbonaceous materials (e.g., char). Plastic-waste-derived char can be used as an additive in epoxy composites to improve the properties and performance of neat epoxy resins. This review compiles relevant knowledge on the potential of additives for epoxy composites originating from plastic waste. It also highlights the potential of plastic-waste-derived char materials for use in materials in various industries.

Selective recovery of caprolactam from the thermo-catalytic conversion of textile waste over γ-Al2O3 supported metal catalysts.

The massive generation of synthetic textile waste has drawn considerable attention. Landfilling/incineration of textile waste has been widely made. To abate the environmental burdensome from the conventional management processes, a thermo-catalytic conversion was used for rapid volume reduction of textile waste and simultaneous valorization by recovering textile monomer in this study. Stockings were chosen as a model feedstock. Because stockings consisted of nylon with other contents, different products (caprolactam (nylon monomer), imines, cyclic dimers, and azepines) were recovered. The yield of caprolactam from the thermal conversion at 500 °C was 53.6 wt%. To selectively enhance the caprolactam yield, catalytic pyrolysis was done using γ-Al2O3 supported metal catalysts (Ni, Cu, Fe, or Co). γ-Al2O3 itself increased the caprolactam yield up to 69.0 wt% via a based-catalyzed reaction of nylon depolymerization and intramolecular cyclization. Under the presence of metal catalysts, the caprolactam yield increased up to 73.3 wt%. To offer desired feature of green chemistry, CO2 was adopted as reactive gas. Under the CO2-mediated catalytic pyrolysis, caprolactam yield was enhanced up to 77.1 wt% over Cu/Al2O3 (basis: stocking mass). Based on the net content of nylon in the stockings, the yield of caprolactam was deemed 95.3 wt%. This study proves that textile waste (stocking) and CO2 are useful resources for recovery of nylon monomer, which can reduce the waste generation with simultaneous recovery of value-added product.

Direct growth of nano-worm-like Cu2S on copper mesh as a hierarchical 3D catalyst for Fenton-like degradation of an imidazolium room-temperature ionic liquid in water.

The increasing consumption of room-temperature ionic liquids (RTILs) inevitably releases RTILs into the water environment, posing serious threats to aquatic ecology due to the toxicities of RTILs. Thus, urgent needs are necessitated for developing useful processes for removing RTILs from water, and 1-butyl-3-methylimidazolium chloride (C4mimCl), the most common RTIL, would be the most representative RTIL for studying the removal of RTILs from water. As advanced oxidation processes with hydrogen peroxide (HP) are validated as useful approaches for eliminating emerging contaminants, developing advantageous heterogeneous catalysts for activating HP is the key to the successful degradation of C4mim. Herein, a hierarchical structure is fabricated by growing Cu2S on copper mesh (CSCM) utilizing CM as a Cu source. Compared to its precursor, CuO@CM, this CSCM exhibited tremendously higher catalytic activity for catalyzing HP to degrade C4mim efficiently because CSCM exhibits much more superior electrochemical properties and reactive sites, allowing CSCM to degrade C4mim rapidly. CSCM also exhibits a smaller Ea of C4mim elimination than all values in the literature. CSCM also shows a high capacity and stability for activating HP to degrade C4mim in the presence of NaCl and seawater. Besides, the mechanistic investigation of C4mim elimination by CSCM-activated HP has also been clarified and ascribed to OH and 1O2. The elimination route could also be examined and disclosed in detail through the quantum computational chemistry, confirming that CSCM is a useful catalyst for catalyzing HP to degrade RTILs.

Applications of agricultural residue biochars to removal of toxic gases emitted from chemical plants: A review.

Crop residues are representative agricultural waste materials, massively generated in the world. However, a large fraction of them is currently being wasted, though they have a high potential to be used as a value-added carbon-rich material. Also, the applications of carbon-rich materials from agricultural waste to industries can have economic benefit because waste-derived carbon materials are considered inexpensive waste materials. In this review, valorization methods for crop residues as carbon-rich materials (i.e., biochars) and their applications to industrial toxic gas removals are discussed. Applications of crop residue biochars to toxic gas removal can have significant environmental benefits and economic feasibility. As such, this review discussed the technical advantages of the use of crop residue biochars as adsorbents for hazardous gaseous pollutants and greenhouse gases (GHGs) stemmed from combustion of fossil fuels and the different refinery processes. Also, the practical benefits from the activation methods in line with the biochar properties were comprehensively discussed. The relationships between the physico-chemical properties of biochars and the removal mechanisms of gaseous pollutants (H2S, SO2, Hg0, and CO2) on biochars were also highlighted in this review study. Porosity controls using physical and chemical activations along with the addition of specific functional groups and metals on biochars have significantly contributed to the enhancement of flue gas adsorption. The adsorption capacity of biochar for each toxic chemical was in the range of 46-76 mg g-1 for H2S, 40-182 mg g-1 for SO2, 80-952 µg g-1 for Hg0, and 82-308 mg g-1 CO2, respectively. This helps to find suitable activation methods for adsorption of the target pollutants. In the last part, the benefits from the use of biochars and the research directions were prospectively provided to make crop residue biochars more practical materials in adsorption of pollutant gases.

Upcycling textile waste using pyrolysis process.

Rapidly changing fashion trends have generated tremendous amounts of textile waste globally. Textile waste is composed of a variety of substances (natural, synthetic, organic, and inorganic fibers). The inhomogeneity and complex nature of textile waste makes recycling economically challenging. Pyrolysis is a thermochemical process that transforms waste feedstocks of an inhomogeneous and complex nature into value added products (i.e., waste upcycling). This article provides a systematic review of the currently available and investigated pyrolysis processes to upcycle textile waste (e.g., material and energy recovery). The challenges in the pyrolysis process of textile waste are discussed, and relevant future research needs are recommended. Despite these challenges, pyrolysis will be an effective end-of-life option for textile waste if continuous research and development activities are conducted.

A polydimethylsiloxane-based sponge for water purification and interfacial solar steam generation.

A better knowledge for the design and synthesis of low-cost, novel porous materials is highly desirable in various fields such as recyclable solar desalination and liquid recycling. Herein, a polydimethylsiloxane-based sponge with a web-like three-dimensional (3D) interconnected porous structure was developed for effective recovery of liquids and the continuous interfacial solar steam generation (ISSG). The sponge is capable of conducting directional transport of oil or organic solvents at temperatures above 32 °C while automatically controlling the desorption of the organic phase below 28 °C. The synergistic combination between high light absorption (above 95 %) and light-to-heat conversion efficiency (99.87 %) resulted in a considerably high seawater evaporation rate (1.66 Kg m-2h-1) under 1 sun. The self-regeneration of the evaporator is facilitated by the salt barrier function of the large channels of the smart sponge with high hydraulic conductivity. This sponge can maintain a maximum evaporation rate up to the 5 consecutive days operation with the co-benefit of real-time regeneration and the reversible switching of the wettability. The reusable smart sponge evaporators are highly efficient in generating clean water from seawater with satisfactory ion rejection rates (above 99.6 %). As such, the prepared sponge shows great potential in environmental restoration, metal recovery, and water regeneration.

Pyrolysis of Denim Jeans Waste: Pyrolytic Product Modification by the Addition of Sodium Carbonate.

Quickly changing fashion trends generate tremendous amounts of textile waste globally. The inhomogeneity and complicated nature of textile waste make its recycling challenging. Hence, it is urgent to develop a feasible method to extract value from textile waste. Pyrolysis is an effective waste-to-energy option to processing waste feedstocks having an inhomogeneous and complicated nature. Herein, pyrolysis of denim jeans waste (DJW; a textile waste surrogate) was performed in a continuous flow pyrolyser. The effects of adding sodium carbonate (Na2CO3; feedstock/Na2CO3 = 10, weight basis) to the DJW pyrolysis on the yield and composition of pyrolysates were explored. For the DJW pyrolysis, using Na2CO3 as an additive increased the yields of gas and solid phase pyrolysates and decreased the yield of liquid phase pyrolysate. The highest yield of the gas phase pyrolysate was 34.1 wt% at 800 °C in the presence of Na2CO3. The addition of Na2CO3 could increase the contents of combustible gases such as H2 and CO in the gas phase pyrolysate in comparison with the DJW pyrolysis without Na2CO3. The maximum yield of the liquid phase pyrolysate obtained with Na2CO3 was 62.5 wt% at 400 °C. The composition of the liquid phase pyrolysate indicated that the Na2CO3 additive decreased the contents of organic acids, which potentially improve its fuel property by reducing acid value. The results indicated that Na2CO3 can be a potential additive to pyrolysis to enhance energy recovery from DJW.

Recent achievements in platform chemical production from food waste.

Food waste conversion/valorization to produce bio-based chemicals plays a key role toward achieving carbon neutrality by 2050. Food waste valorization to renewable chemicals is thus an attractive and eco-friendly approach to handling food waste. The production of platform chemicals from food waste is crucial for making highly value-added renewable chemicals. However, earlier reviews dealing with food waste valorization to produce value-added chemicals have emphasized the enhancement of methane, hydrogen, and ethanol production. Along these lines, the existing methods of food waste to produce platform chemicals (e.g., volatile fatty acids, glucose, hydroxymethylfurfural, levulinic acid, lactic acid, and succinic acid) through physical, chemical, and enzymatic pretreatments, hydrolysis, fermentation, and hydrothermal conversion are extensively reviewed. Finally, the challenges faced under these methods are discussed, along with suggestions for future research on platform chemical production from food waste.