Hydroxypropyl methylcellulose (HPMC) is a cellulose derivative characterized by physicochemical properties (gel formation, water solubility, biodegradability, and biocompatibility). These properties explain their wide use in industries such as pharmaceuticals, food, and construction. This review evaluates the classification, production processes, and analytical characterization of HPMC, with particular attention to its versatility and sustainability life cycle. The environmental impact of HPMC is analyzed through its energy-intensive production, waste generation, emissions, and end-of-life biodegradability. In comparison with many petroleum-based polymers, HPMC is often considered a greener option and its use as an additive in modern chemical industry is extended. Therefore, the adoption of more sustainable production practices is essential to minimize its ecological footprint. In this sense, greener raw material sourcing, improved production process efficiency, lower emission etherification and purification routes, and broader implementation of life-cycle-based optimization strategies were identified as key priorities to be addressed.

This chapter provides an integrated analysis of simulation tools, kinetic modeling, and sustainability assessment applied in studies of biodiesel production from waste cooking oils. Kinetic parameters, simulation tool selection, and process sustainability are considered. The recent (2019-2026) technical, computational, and policy-related challenges affecting the simulation realism, data availability, and model scalability in biodiesel production from waste cooking oil by transesterification are identified. Simulation challenges are also discussed. Three research gaps are identified: lack of cross-study harmonization of kinetic parameters, absence of a structured mapping between simulation tools and their functional applicability, and disconnect between reported kinetic models and the explicit identification of which model assumptions limit scalability. This chapter fits under the SDG 7 (Affordable and Clean Energy), SDG 9 (Industry, Innovation and Infrastructure), SDG 12 (Responsible Consumption and Production), and SDG 13 (Climate Action).

Mesoporous zeolitic imidazolate framework (ZIF)-supported transition metal photocatalysts have been recognized as suitable catalysts because of their high surface area, porous structure, good chemical stability and enhanced mass transport capability. Despite various literature reviews on ZIF-based photocatalysts, there is no thorough evaluation of mesoporous ZIF-supported transition metals and their modification techniques for organic pollutant removal from water. In this review, the recent achievements in the design, modification and application of mesoporous ZIF-based transition metal photocatalysts in wastewater treatment are highlighted. Initially, the basic concepts of photocatalysis and mechanisms responsible for photocatalytic degradation of organic pollutants are highlighted before presenting a brief introduction on ZIF structures and types, highlighting the importance of mesoporous ZIFs in efficient charge and reactant transportation. The review further emphasizes various techniques used for modification of mesoporous ZIF-based transition metals. As shown by recent achievements, the incorporation of transition metal photocatalysts, including TiO2, ZnO, WO3, ZnS, CdS and Ag2S into mesoporous ZIFs results in considerable improvements in terms of visible light absorption, charge separation, photocatalytic efficiency and the reusability of the catalysts in dye decomposition, decontamination of pharmaceutical drugs and removal of various organic pollutants. At last, recent problems with the stability, scalability of synthesis and fundamental mechanisms of action are thoroughly examined, while future prospects regarding rational mesopore engineering, interface design and multifunctional hybrid structures are outlined.

Photocatalysis and piezo-photocatalysis are two advanced oxidation processes (AOPs) that have shown promise for eliminating some stubborn pollutants such as organic dyes and antibiotics, which are among the most commonly reported contaminants in wastewater from hospitals, pharmaceuticals and textile industries. Because of its special combination of ferroelectricity, strong internal electric fields, adjustable band configuration and superior chemical stability, barium titanate (BaTiO3), a traditional ferroelectric perovskite semiconductor, has recently drawn a lot of interest for environmental uses. Because of these characteristics, BaTiO3 and based materials are very appealing for improving charge separation, increasing the production of reactive oxygen species (ROS) and attaining better catalyst efficiency. The structural parameters, electrical behaviour and ferroelectric-piezoelectric properties of BaTiO3 are all covered in this review, which is followed by an extensive description of photocatalytic and piezo-photocatalytic breakdown mechanisms. To illustrate their impact on morphology, crystallinity and catalytic performance, several synthesis and processing techniques—such as hydrothermal, ultrasonication, precipitation and calcination approaches—are critically contrasted. The recent developments in BaTiO3-based photocatalytic materials and their uses in antibiotic and dye degradation are methodically examined and summarized in this review. Lastly, this review highlights the main problems with BaTiO3, namely its limited ability to absorb visible light, its scalability and stability, and it suggests future research avenues for creating more advanced BaTiO3-based materials for effective and sustainable water treatment.

In this review, the optimal conditions of transesterification of waste cooking oil to produce biodiesel are examined, including methanol:oil ratio, catalyst concentration, reaction temperature, and reaction time. Within the scope of this review, the key process parameters include feedstock type, catalyst selection, reaction conditions, and biodiesel yield across different sources. This review consolidates the recent findings (inclusive of data for 2025) reported in one place, highlighting common trends, discrepancies, and research gaps. For this review, a critical analysis was conducted to assess the scientific and engineering challenges, particularly in catalyst efficiency, pretreatment methods, and economic feasibility. The key findings are identified to be a lack of economic and environmental data that could assist in formulating potential largescale waste cooking oil transesterification systems for biodiesel production. Studies report varying conditions, hindering the establishment of a standardized process for maximizing biodiesel production efficiency. Factors such as feedstock availability, catalyst recyclability, and energy consumption require further study to determine the long-term feasibility of biodiesel from waste cooking oil as a sustainable alternative to fossil fuels. Addressing these issues is crucial for optimizing transesterification of waste cooking oil for biodiesel production at an industrial scale. The findings highlight the need for optimized transesterification parameters, cost-effective catalysts, and scalable pretreatment methods to enhance biodiesel yield, reduce production costs, and improve economic and environmental sustainability for industrial applications.

The treatment of laundry wastewater, a source of complex and hazardous pollutants, remains a pressing environmental challenge. Three waste-derived biochars produced from pruning waste (P-BC), almond shells (A-BC), and stabilized organic fraction (S-BC), were used in a packed column configuration, for the treatment of synthetic laundry wastewater (SLW) with high colour number (CN = 17.8 m(-1)) and COD (approximate to 100 mg/L), obtained by the washing of imported textiles. Adsorption performance was evaluated via UV-Vis spectroscopy and correlated with detailed material characterization (XRD, FT-IR, SEM-EDX, CHNS analysis). All BCs showed a disordered graphitic structure, while A-BC and S-BC specifically contained inorganic crystalline compounds. SEM analysis evidenced a channel-like structure for P-BC; ridges and flat areas on the surface of A-BC; roundish pores alongside with straight and zigzagged channels for S-BC. FT-IR spectra revealed surface hydroxyl, aliphatic and aromatic groups in all BCs. Specific surface area resulted approximate to 245, 212, 344 m(2)/g for P-BC, A-BC and S-BC respectively. S-BC exhibited the highest efficiency (99% of colour and 98% of organic matter removal) within 120 min, at differente pH values (3 & 9). Ecotoxicity assays showed that SLW was highly toxic in all life stages of Artemia franciscana, while the mortality was significantly reduced in the treated effluents. None of the biochar exhibited acute toxicity, confirming their environmental compatibility. Waste-based biochars, particularly S-BC, can serve as efficient, scalable, and environmentally safe materials for column-based treatment of laundry wastewater, offering a promising route toward integrating low-cost adsorption processes into decentralized wastewater reuse treatment plants.

Within the framework of circular economy, three waste-derived biochars (BCs) obtained from pruning residues (P-BC), almond shells (A-BC), and the stabilized organic fraction of municipal solid waste (S-BC) were investigated as sustainable adsorbents for the removal of chloramphenicol (CAP) from aqueous solutions, the ecotoxicological safety of the treated effluents was evaluated as well. BCs were characterized by Scanning Electron Microscope (SEM), Energy Dispersive X-Ray Spectroscopy (EDX), X-Ray Diffraction (XRD), Fourier Transform-Infrared Spectroscopy (FT-IR), Brunauer-Emmet-Teller method (BET), and proximate analyses exhibiting distinct structural and surface characteristics. S-BC showed the highest specific surface area (344 m2/g) and pore volume, whereas XRD and FT-IR analyses revealed the presence of mineral phases, mainly calcite, in A-BC and S-BC. All materials displayed a high volatile matter content (up to 73.3 %). P-BC, A-BC and S-BC allowed up to 95 %, 83 % and 96 % of CAP removal, respectively. Equilibrium and kinetic modelling indicated that adsorption involved multiple interacting mechanisms associated with surface interactions and diffusion phenomena. S-BC exhibited the highest adsorption capacity (122.0 mg/g), which was attributed to its more developed porous structure and favourable surface properties. Ecotoxicological assays revealed CAP’s clear dose-dependent toxicity toward Artemia franciscana. None of the BCs showed intrinsic toxicity (p > 0.05), while treated effluents significantly reduced CAP-induced mortality at low and moderate pollutant concentrations. At higher CAP concentrations, the progressive saturation of adsorption sites resulted in lower removal efficiencies and reduced detoxification performance. BCs, particularly S-BC, represent promising circular-economy materials for the treatment of antibiotic-contaminated waters.

This article aims to: (i) revisit the Temkin adsorption isotherm employed for adsorption data modeling in many publications, (ii) to concisely describe the recently nonlinear Temkin adsorption isotherm model developed by Chu (2021), and (iii) and to re-correlate the equilibrium adsorption data from published studies to this recent Temkin adsorption isotherm and recalculate the values of the fitting parameters. The values of the Temkin isotherm constant (also designated the equilibrium binding constant) obtained from the two correlation approaches applied in this work may differ significantly. This newly proposed Temkin adsorption isotherm can be important in some practical cases. Such a case can be when a laboratory-scale batch aqueous-phase adsorption process, which is predominantly captured by the newly proposed Temkin adsorption isotherm, is being scaled-up to its slurry contact adsorption.

In this article, more than fifty publications (2021–2025) have been reviewed to analyze the adsorption behaviors of ionic liquid-based materials for different water contaminants under varied environmental conditions. Thus, the trends observed across the removal performances for different pollutant classes are depicted, and the common interaction mechanisms related to material reusability as an adsorbent are discussed. The main observations we drew from this review are as follows: (i) Ionic liquid-based materials show significant promise as effective scavengers of aqueous pollutants by adsorption because they have relatively high adsorption capacities and good recyclability of five cycles of reuse and more, (ii) support-immobilized ionic liquid-based materials show enhanced material stability, reusability, and adsorption efficiency for aqueous adsorbates, (iii) however, there are key challenges that persist, and these cover aspects related to ionic liquid stability, environmental safety, and real-water applicability of these ionic liquid-based materials under harsh environmental conditions, and (iv) lifecycle-based techno-economic studies of ionic liquid-based adsorption units is necessary if ionic liquid-based materials are being contemplated for industrial water treatment processes. This review also identifies current research gaps around the development of more efficient, durable, and sustainable ionic liquid-based adsorption systems for water purification. The major implication of developing ionic liquid-based aqueous-phase adsorbents is to promote green chemistry at the laboratory scale and aspire for green chemical process engineering in real-world water remediation systems using such a material that has the requisite selectivity and durability.

Polyhydroxyalkanoates have been investigated as biodegradable adsorbents in water treatment; yet, their widespread application remains restricted. Particularly when combined with nanocomposites, their adjustable porosity and tunable chemical structure offer the possibility to enhance adsorption, thereby improving the efficiency and selectivity of aqueous-phase solute removal. Nevertheless, industrial adoption and use of polyhydroxyalkanoates as aqueous-phase adsorbents are impeded by obstacles such as scalability, high production costs, and stability in harsh real conditions. This concise review examines current laboratory-scale research developments in polyhydroxyalkanoate-based materials used as adsorbents for aqueous-phase solutes, including aspects related to microbial engineering for cost efficiency, sophisticated surface modifications for enhanced adsorption, and pilot-scale analyses to determine feasibility. At the pilot scale, implementating the use of polyhydroxyalkanoate-based materials as aqueous-phase adsorbents is hindered by long hydraulic residence times, structural instability due to operational conditions, and cost-intensive production and extraction methods. Additionally, adsorption kinetics exhibited by polyhydroxyalkanoate-based materials used as adsorbents vary across aqueous-phase systems, and their adsorption performance declines under mixed-solute conditions as a result of competitive binding. Consequently, in a stronger spirit of developing sustainable water remediation technologies, more interdisciplinary research addressing these multiple challenges could be expected to enhance the viability of polyhydroxyalkanoate-based materials as effective adsorbents in water treatment. It is also crucial to reassess the plausible premature biodegradation of these materials whenever they are to be contacted with microbe-laden real wastewaters. It might then be important to design an effective in-built protection/deprotection mechanism to ward off such degradation prior to the polyhydroxyalkanoate-based materials fulfilling their intended adsorption purpose in a contaminated aqueous milieu.

Sustainable energy production and effective water pollution control are critical global priorities. Harmful algal blooms (HABs) and waterborne pathogens pose significant threats to water quality and public health, necessitating efficient and eco-friendly treatment methods. Transition metal-based photocatalytic heterojunctions offer promising solutions by leveraging the unique properties of transition metals to enhance photocatalytic efficiency. This review examines recent advances in these heterojunctions employed for algal inhibition and water disinfection, discussing various heterojunction type (including conventional, p-n, Z-scheme, S-scheme, and Schottky heterojunctions), and their synthesis methods. We elucidate the mechanisms involved, highlighting improved electron transfer, reduced recombination rates, and broadened light absorption. Recent studies on their effectiveness in inhibiting harmful algae and disinfecting water are also reviewed. Current challenges and future research directions to optimize these materials are identified. This is a first comprehensive overview focusing on the contributions of transition metals in photocatalytic heterojunctions for water treatment, aiming to support the development of sustainable technologies.

Here, we offer thoughts concerning a 'zero residual nanoadsorbent toxicity' environmental policy which we strongly advocate. Our discussions in support of this policy are based on the adage 'Prevention is better than cure'. Besides emphasizing the need for strict regulations (regional and international), research and development avenues are highlighted for the technology that can achieve 'zero tolerance' for residual nanoadsorbent levels escaping and building up in receiving ecosystems. We do not oppose nanoadsorbents. On the contrary, their water and wastewater purification potentials are well recognized. However, they should not be permitted to translocate downstream from the exit point of a final effluent.

Adsorption parameters (e.g. Langmuir constant, mass transfer coefficient and Thomas rate constant) are involved in the design of aqueous-media adsorption treatment units. However, the classic approach to estimating such parameters is perceived to be imprecise. Herein, the essential features and performances of the ant colony, bee colony and elephant herd optimisation approaches are introduced to the experimental chemist and chemical engineer engaged in adsorption research for aqueous systems. Key research and development directions, believed to harness these algorithms for real-scale water treatment (which falls within the wide-ranging coverage of the Sustainable Development Goal 6 (SDG 6) 'Clean Water and Sanitation for All'), are also proposed. The ant colony, bee colony and elephant herd optimisations have higher precision and accuracy, and are particularly efficient in finding the global optimum solution. It is hoped that the discussions can stimulate both the experimental chemist and chemical engineer to delineate the progress achieved so far and collaborate further to devise strategies for integrating these intelligent optimisations in the design and operation of real multicomponent multi-complexity adsorption systems for water purification.

In this article, three mistakes detected in the published article “Removing fluoride ions from wastewater by Fe3O4 nanoparticles: Modified Rhodophytes (red algae) as biochar” by Hota et al. (Journal of Water Process Engineering 58 (2024) 104776) in the adsorption isotherm modeling of aqueous-phase equilibrium adsorption data are first pointed out. Thereafter, calculations have been performed afresh, and new correct correlations of the Langmuir, Freundlich and Temkin isotherms to the experimental adsorption data reported in Hota et al. are obtained. The corresponding results of the correct data analysis and adsorption isotherm modeling differ significantly from those reported primarily in Hota et al. The objective lesson to be learnt from this article is that the need for performing correct adsorption isotherm correlation in aqueous-phase adsorption science cannot be emphasized enough.

The analysis of aqueous adsorption data comprises adsorbent characterization, bench-scale batch and fixed bed adsorption experiments, adsorption kinetics modeling, adsorption isotherm analysis using predefined models, and thermodynamics analysis. Then, a plausible adsorption interaction (often called a ‘mechanism’) is proposed. Adsorption literature abounds with original research articles written based on this overall approach. However, a cluster of recent articles have boldly presented several critical flaws within these established adsorption data modeling and analyses. We summarize and revisit salient points discussed in them to sound the alarm for using the proposed corrected approaches in adsorption data modeling and analysis. Unfortunately, these corrections are usually neglected in the adsorption literature. Hence, this article issues a warning that cannot be overemphasized, advocating correct adsorption data modeling and analyses. It is high time to put the correct mathematical approach to adsorption data modeling and analysis in practice. The core benefits minimize future errors to reach the correct conclusions and to designing more effective water purification adsorption units.

Pore network, pore connectivity, and the resulting effective adsorbate pore diffusivity within an adsorbent are critical physical considerations in mass transport modeling of aqueous adsorption. Tied to these three adsorbent features are the adsorbent tortuosity and tortuosity factor concepts. These concepts encompass the collective hindrance to intra-adsorbent adsorbate transport arising because of a disorderly adsorbent porous topology. It is crucial for materials scientists, chemists, chemical engineers, and water treatment specialists to understand the complex and variable connections among adsorbate chemistry, adsorbent chemistry, adsorbent porosity, pore shape, size, and tortuosity, pore wall effect, adsorbate-adsorbent interactions, and adsorbate-adsorbate interactions in competitively contaminated aqueous environments. Adsorbent tortuosity has been sporadically studied in aqueous adsorption models. Despite the small population of these studies, insightful observations and inferences have been reported. However, as it appears, no review has been published to compile, compare, and contrast these aspects. Hence, this review concisely brings up those observations and interpretations around adsorbent tortuosity for aqueous adsorption systems. The notion of an adsorbent's tortuosity being single-valued is argued to be imprecise. Finally, perspectives are aired on possible research and development directions for elucidating the dynamic attributes of adsorbent tortuosity and applying them in real-scale adsorption-oriented water purification. The data acquired by filling in these research gaps can enable the design of adsorbents more adapted for real-scale water purification.

Dissolved solute uptake from aqueous solutions by adsorbents has been studied for decades at laboratory-scale. We revisit key points raised by others and then discuss the degree of phenomenological analogy between gas-phase and aqueous-phase adsorptions, and the probable origin and validity of using 8 kJ mol-1 for the characteristic free energy of adsorption (E) when assigning physical adsorption versus chemical adsorption to an aqueous-phase adsorption using the Dubinin-Radushkevich (D/R) model. We demonstrate that E = 8 kJ mol-1 is misfitted for use with these models for assigning 'chemisorption' versus 'physisorption' to an aqueous-phase adsorption. Solvent-related processes occurring in aqueous media are not explicitly considered in aqueous-phase D/R models. We introduced a new parameter (gamma corr) in the expression for the Polanyi adsorption potential (epsilon) in the aqueous-phase D/R model. The introduction of gamma corr in this model is novel to the adsorption literature. gamma corr serves as a net activity coefficient for the entire range of intramolecular and intermolecular thermodynamic interactions occurring during a solidaqueous interfacial adsorption. Thus, epsilon becomes RT ln(gamma corr center dot cs/ce). For twelve experimental aqueous-phase adsorption data sets we examined, gamma corr varied from 0.023 to 2.198. Using RT ln(gamma corr center dot cs/ce) improved the prediction of these experimental aqueous-phase adsorption data. (c) 2023 Institution of Chemical Engineers. Published by Elsevier Ltd. All rights reserved.

Nanotechnology that is based on phytobiomass is a technique that has the potential to play a major role in wastewater treatment since it is environmentally friendly, easy to deploy, and cost-effective. This technology employs plant parts such as leaves, flowers, stems, seeds and roots, and agricultural wastes to synthesize nanoadsorbents. These nanoadsorbents have unique properties, such as smaller size, higher surface-volume ratio, magnetic behaviour, thermal stability, selectivity, porous structure, surface functionalization, catalytic properties and target-specific capabilities, which make them an attractive material for removing ‘Emerging Contaminants’ from contaminated water and wastewater. Pharmaceuticals, personal care products, endocrine disruptors, surfactants, disinfectants, flame retardants and pesticides are the various classes of emerging contaminants used almost every day globally. Adsorption is one green and sustainable technology that has shown excellent performance when employing nanoadsorbents to purify contaminated water. It is an effective and efficient technology for removing emerging contaminants that inform polluted water or wastewater to restore water quality. This review aims to summarize the current research progress in the use of different nanoadsorbents synthesized from various plant parts for removing aqueous emerging contaminants.

Attrition resistance in an adsorbent is one measure of its mechanical strength. It quantifies its ability to resist the impact of frictional forces generated in a milieu where hydrodynamic agitation exists. However, attrition resistance has been only sporadically examined in adsorbents used to remove aqueous adsorbates. Since attrition is relevant in aqueous adsorption process design, this review discusses the quantification of attrition resistance, variability in loss due to attrition across adsorbents, and the implications of attrition on adsorption systems. Finally, some key research opportunities that could be explored for a better understanding of attrition in real-scale water purification are presented. It is inferred that substantial research and development still needs to be accomplished to better understand the attrition resistance-adsorbent behavior within real-scale aqueous adsorption environments. The results can be harnessed to design and produce more robust, efficient and cost-effective adsorbents.

It is the purpose of this paper to investigate the data fitting attributes of the exponential integral isotherm, which was first derived by Ruthven in 2004 to describe adsorption at gas–solid interfaces. The exponential integral isotherm, a variant of the virial isotherm, incorporates the two fitting parameters of the Langmuir isotherm and has an expandable mathematical structure. It has lain dormant for nearly 20 years. This fact may seem surprising considering the versatility of the isotherm, as will be shown in this work. A slightly modified form of the exponential integral isotherm, called the Ruthven–virial isotherm, is used in this work to interpret previously published aqueous-phase isotherm data. It is observed that the Ruthven–virial isotherm is capable of accurately tracking experimental adsorption isotherms with and without an apparent plateau. The Freundlich isotherm is good at describing data without a plateau, while the Langmuir isotherm excels at fitting data with a plateau. The Ruthven–virial isotherm combines the individual strengths of the Freundlich and Langmuir isotherms into a single model. Furthermore, it is shown that the data fitting performance of the two-parameter Ruthven–virial isotherm is comparable to that of the three-parameter Sips isotherm. The Ruthven–virial isotherm is a hidden gem and a practical alternative to the Freundlich and Langmuir equations in the correlation of hyperbolic adsorption isotherms. We hope that the findings presented here will inspire the research community to evaluate the Ruthven–virial isotherm in the modeling of contaminant adsorption at aqueous-solid interfaces.