The effect of fatty acid type bonded to chitosan on the emulsifying properties of chitosan-based particles was investigated. Capric acid, myristic acid, and stearic acid were attached to chitosan ...chains. Longer fatty acids in the structure of chitosan lead to the better and more uniform formation of chitosan nanogels. The contact angle of chitosan, chitosan-capric acid, chitosan-myristic acid and chitosan-stearic acid were found to be 52.5°, 60.0°, 65.1° and 72.5°, respectively. Different chitosan nanogels were used to stabilize walnut oil emulsions, and the emulsion stabilized with chitosan-stearic acid nanogels had the lowest creaming index (15.2%). Stabilized emulsions with chitosans attached to longer chain acids were more adapted to the mechanism of Pickering emulsions, in addition to having higher viscosity as well as more gel-like behavior. In general, this study showed that emulsifying properties of chitosan could be improved by increasing the number of fatty acid carbons bonded to chitosan.
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•Covalent crosslinking was generated between different fatty acids and chitosan.•Chitosan-stearic acid nanogels had the highest hydrophobic property.•Walnut oil-in-water Pickering emulsion stabilized by different chitosan nanogels.•Emulsion stabilized by Chitosan-Stearic acid nanogels had a more stable and gel-like behavior.
Nowadays, a growing number of microplastics are released into the environment due to the extensive use and inappropriate management of plastic products. With the increasing body of evidence about the ...pollution and hazards of microplastics, microplastics have drawn major attention from governments and the scientific community. As a kind of emerging and persistent environmental pollutants, microplastics have recently been detected on a variety of substrates in the world. Therefore, this paper reviews the recent progress in identifying the sources of microplastics in soil, water, and atmosphere and describing the transport and fate of microplastics in the terrestrial, aquatic and atmospheric ecosystems for revealing the circulation of microplastics in the ecosystem. In addition, considering the persistence of microplastics, this study elucidates the interactions of microplastics with other pollutants in the environment (i.e., organic pollutants, heavy metals) with emphasis on toxicity and accumulation, providing a novel insight into the ecological risks of microplastics in the environment. The negative impacts of microplastics on organisms and environmental health are also reviewed to reveal the environmental hazards of microplastics. The knowledge gaps and key research priorities of microplastics are identified to better understand and mitigate the environmental risks of microplastics.
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•Source, transport and fate of microplastics are comprehensively reviewed.•Interaction between microplastics and other environmental pollutants is discussed.•Environmental risks and negative impacts of microplastics are discussed.•Knowledge gaps and research priorities of microplastics are presented.
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•Eight conversion routes for waste residues using microwave-assisted heating are reviewed.•Microwaves’ high energy use was offset by shorter duration and better product ...quality.•MW-assisted pyrolysis is the most studied route while other routes are still undermined.•Catalysis and co-processing of two wastes are the recent trends with several routes.•MW-assisted pyrolysis in a vacuum environment is one of the most recent advancements.
With drastic fossil fuel depletion and environmental deterioration concerns, a move towards a more sustainable bioenergy-based economy is essential. Lately, the application of microwave (MW) irradiation for waste processing has been attracting interest globally. MW-assisted heating possesses several advantages such as the provision of high microwave energy into dielectric materials with deeper penetration for internal heat generation, showing beneficial features in improving the heating rate and reducing the reaction time. Consequently, the most recent literature regarding the applications of MW-assisted heating for biomass pretreatment as well as biofuel and bioenergy production was reviewed and consolidated in this study. An impressive increase in the product yield and improvement of the product properties are reported, with the use of MW-assisted heating in several conversion routes to produce biofuels. Despite being a promising technology for biofuel production, some major fundamental data of MW-assisted heating have not been comprehensively identified. Therefore, the feasibility of this technology for large-scale implementation is still subpar. Understanding the interaction between the feedstock and the microwave electromagnetic field, and the optimization of several operational and mechanical parameters are the two main keystones that would propel the industrialization of MW heating in the near future. This provides key insights leading to increased feasibility and more advanced application of MW heating.
This study reports a novel method using microwave vacuum pyrolysis combined with sodium-potassium hydroxide mixture (NaOH-KOH) activation to produce highly porous activated carbon (AC) from palm ...residue (i.e. palm kernel shell, PKS) – a solid residue constantly produced in large volume by palm industry. The yield and properties of AC produced were found significantly influenced by two key process parameters - type of activating agent and chemical impregnation ratio. The pyrolysis provided fast heating rate (60 °C/min), high temperature (607 °C), and short process time (35 min) to convert PKS into biochar, and the subsequent activation by NaOH-KOH mixture at 1.0 of chemical impregnation ratio resulted in 84 wt% yield of AC. The AC possessed high BET surface area (1320 m2/g) and highly porous structure formed by micro- and meso-pores, thus showing high adsorption capacity. The adsorption capacity of AC was examined via impregnation with nickel and aluminium atoms (termed “Ni/AC” and “Al/AC”) followed by application in treating industrial effluent abundantly released from palm oil mill (termed ‘palm oil mill effluent, POME). Both Ni/AC and Al/AC showed high removal efficiency in reducing the total suspended solid (TSS), oil and grease (O&G), biochemical (BOD) and chemical oxygen demand (COD) in POME. Higher removal efficiency on BOD and COD was observed for Ni/AC and Al/AC than normal AC (non-metallic AC). The production cost of AC using this pyrolysis method was estimated to be ranged from 4 to 10 USD/kg. The results show the exceptional promise of this pyrolysis method as an approach to transform PKS into highly porous AC for utilize as an adsorbent to treat POME.
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•Microwave vacuum pyrolysis combined with NaOH-KOH activation was reported.•Two process parameters were examined for the yield and properties of AC produced.•AC was upgraded into metallic AC (Al/AC and Ni/AC) to treat palm oil mill effluent.•Metallic AC removed 85% of BOD and 89% of COD concentrations.•Normal AC (non-metallic) showed higher removal rate of TSS (80%) and O&G (88%).
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•There is a global need to use plants to restore the ecological environment.•Here we conduct a systematic review of phytoremediation mechanisms and it’s the parameters.•Plants mainly ...use their own metabolism including the interaction with microorganisms.•This is affected by light intensity, stomatal conductance, temperature and microbial species.•Further research is needed to study the effects of catalysts in phytoremediation.
There is a global need to use plants to restore the ecological environment. There is no systematic review of phytoremediation mechanisms and the parameters for environmental pollution. Here, we review this situation and describe the purification rate of different plants for different pollutants, as well as methods to improve the purification rate of plants. This is needed to promote the use of plants to restore the ecosystems and the environment. We found that plants mainly use their own metabolism including the interaction with microorganisms to repair their ecological environment. In the process of remediation, the purification factors of plants are affected by many conditions such as light intensity, stomatal conductance, temperature and microbial species. In addition the efficiency of phytoremediation is depending on the plants species-specific metabolism including air absorption and photosynthesis, diversity of soil microorganisms and heavy metal uptake. Although the use of nanomaterials and compost promote the restoration of plants to the environment, a high dose may have negative impacts on the plants. In order to improve the practicability of the phytoremediation on environmental restoration, further research is needed to study the effects of different kinds of catalysts on the efficiency of phytoremediation. Thus, the present review provides a recent update for development and applications of phytoremediation in different environments including air, water, and soil.
This paper begins with a review on the current techniques used for the treatment and recovery of waste oil, which is then followed by an extensive review of the recent achievements in the sustainable ...development and utilization of pyrolysis techniques in energy recovery from waste oils. The advantages and limitations shown by the use of pyrolysis technique and other current techniques were discussed along with the future research that can be performed on the pyrolysis of waste oil. It was revealed that the current techniques (transesterification, hydrotreating, gasification, solvent extraction, and membrane technology) are yet to be sustainable or completely feasible for waste oil treatment and recovery. It was established that pyrolysis techniques offer a number of advantages over other existing techniques in recovering both the energetic and chemical value of waste oil by generating potentially useful pyrolysis products suitable for future reuse. In particular, microwave pyrolysis shows a distinct advantage in providing a rapid and energy-efficient heating compared to conventional pyrolysis techniques, and thus facilitating increased production rates. It was found that microwave pyrolysis of waste oil showed good performance with respect to product yield, reaction time, energy consumption, and product quality, and thus showing exceptional promise as a sustainable means for energy recovery from waste oils. Nevertheless, it was revealed that some important characteristics of the pyrolysis process have yet to be fully investigated. It was thus concluded that more studies are needed to extend existing understanding in the optimal reaction and process parameters in order to develop the pyrolysis technology to be a sustainable and commercially viable route for energy recovery from problematic waste oils.
Summary
There are various methods to produce hydrogen from water splitting as a substitute energy resource for fossil fuels in accordance with the global environmental crisis. Among these, water ...photocatalysis is considered one of the most renewable and sustainable processes simulated the solar energy utilized system in nature. During a half century, different kinds of photocatalysts were developed to convert photon energy into chemical energy to induce redox potential under visible light irradiation condition. In the beginning step, semiconductor materials, such as transition metal oxides, were explored extensively to use as a photocatalyst for hydrogen generation. However, semiconductor has limitations to act as an effective photocatalyst for water splitting due to the large band gap and recombination of charge carriers. Therefore, several kinds of modifications of structure or components have been studied to design visible light active photocatalysts for water splitting to generate hydrogen. Their performance was improved substantially by adding a noble metal or sensitizer to adjust the band gap and reduce the recombination of photoinduced charge carriers. Considering solar light‐induced photocatalytic hydrogen generation, various visible light active photocatalysts have been derived from carbon chain organic compounds and lattice crystals. This review classifies the visible light active photocatalysts as follows: (a) structural and chemical components of modified graphitic carbon nitride (g‐C3N4), (b) exfoliated perovskites, and (c) π‐bond conjugated polymers to produce hydrogen from water splitting. The hydrogen evolution efficiency of photocatalysts shows a great difference under visible light (λ > 400 nm) irradiation according to the three‐dimensional structure and electron transfer pathway. This is because the capability of restricting the recombination of photoinduced charge carriers and the band gap between the valence band and the conduction band of photocatalysts is dependent on the morphology and electrostatic interactions among components. This paper reviews visible light photocatalysts, that is, g‐C3N4 based materials, layered perovskites, and conjugated polymers, to provide integrated insight into photocatalytic water splitting to obtain hydrogen.
A variety of methods to produce hydrogen energy from water splitting as a substitute energy resource of fossil fuels have been reported. Among these, water photocatalysis is regarded as one of the most renewable and sustainable processes. In this work, based on recently published literature, visible light photocatalysts that is, g‐C3N4 based materials, layered perovskites, and conjugated polymers are reviewed to provide integrated insight regarding photocatalytic water splitting to obtain hydrogen.
A sustainable management of environment and agriculture is crucial to protect soil, water, and air during intensified agriculture practices as well as huge industrial and transportation activities. A ...promising tool to address these challenges could be the application of biochar, a carbonaceous product of biomass pyrolysis. The efficiency of biochar could be improved through physical, chemical and microbial procedures. Engineered biochar could then be applied for various applications ranging from sustainable agriculture to pollution remediation and catalytic reactions. Biochar engineering allows achieving biochar properties which are optimum for specific applications and/or under specific conditions. This would lead to harnessing the favorable features of biochar and to enhance its efficiency while simultaneously minimizing the existing tradeoffs. This review covers the production and applications of engineered biochar by summarizing great deals of research and knowledge on the field. Unlike previous reviews, herein biochar physical and chemical properties and the factors affecting them (i.e., biomass nature and pyrolysis conditions) have been discussed in detail. Moreover, the contributions of each physical and chemical activation/modification method to improving biochar characteristics with respect to environmental applications have been specifically scrutinized. By providing the state-of-the-art knowledge about engineered biochar production, properties, and applications, this review aims to help research in this field for identification of the culprits that must be addressed in future experiments.
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•Detailed physical and chemical properties of biochar have been discussed.•Engineering biochar production techniques improve biochar’s properties and efficiency.•Biomass composition and pyrolysis conditions mainly control biochar properties.•Active sites and functional groups could be enriched in engineered biochar.•Inappropriate biochar applications may lead to negative effects on the environment.
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•Activated carbon (AC) was produced by microwave pyrolysis with hydroxide mixture.•Four process parameters were examined for the yield and properties of AC produced.•AC showed ...micro-mesoporous structure with high surface area and pore volume.•AC showed 90% removal of malachite green dye present in textile wastewater.•Activation with metal hydroxide mixture produces high-grade AC as dye adsorbent.
A micro-mesoporous activated carbon (AC) was produced via an innovative approach combining microwave pyrolysis and chemical activation using NaOH/KOH mixture. The pyrolysis was examined over different chemical impregnation ratio, microwave power, microwave irradiation time and types of activating agents for the yield, chemical composition, and porous characteristic of the AC obtained. The AC was then tested for its feasibility as textile dye adsorbent. About 29 wt% yield of AC was obtained from the banana peel with low ash and moisture (<5 wt%), and showed a micro-mesoporous structure with high BET surface area (≤1038 m2/g) and pore volume (≤0.80 cm3/g), indicating that it can be utilized as adsorbent to remove dye. Up to 90% adsorption of malachite green dye was achieved by the AC. Our results indicate that the microwave-activation approach represents a promising attempt to produce good quality AC for dye adsorption.
Fruit wastes of mango endocarp and waste fruits peel from banana, orange and watermelon were pyrolysed respectively and subjected to different analyses to examine their thermal behaviour, chemical ...functional group, elemental and proximate content. The fruit wastes were dominated by volatile matter (52–67 wt%) containing aliphatic hydrocarbons, fatty acids and lignocellulosic components that can be recovered as potential fuel or chemical feedstock via pyrolysis. The wastes were also detected to have considerable amounts of fixed carbon (30–36 wt%), thus showing potential to be pyrolysed to produce biochar for use as activated carbon or catalyst support. The wastes can be pyrolysed at ≥ 400 °C to convert the majority of the waste content into volatiles for recovery as useful bio-oil and bio-gas, and the remaining solid mass can be recovered as bio-char. The results demonstrate that the fruit wastes show exceptional promise as a feedstock for pyrolysis conversion into potentially useful products.
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•Fruit wastes were examined for their potential as feedstock for pyrolysis recovery.•Wastes were also pyrolysed and examined for thermal behaviour via TGA approach.•Wastes contain high volatile matter with aliphatics, fatty acids, lignocellulose.•Wastes show high fixed carbon content for recovery as biochar via pyrolysis.•Pyrolysis at ≥400 °C is suitable to recover the majority of the waste content.
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