ABSTRACT This review examines the contributions of alternative nuclear fuels and advanced reactor technologies to enhancing the sustainability, safety, and resource efficiency of nuclear energy systems during the transition to a low‐carbon future. A thorough synthesis of the existing literature was undertaken, with an emphasis on Thorium‐based fuels, uranium‐233, minor actinides, and innovative reactor configurations encompassing molten salt reactors (MSRs), small modular reactors (SMRs), and fast breeder reactors (FBRs). The investigation integrates various dimensions, including technical performance metrics, fuel cycle attributes, environmental ramifications, and pertinent global policy frameworks. MSRs exhibit thermal efficiencies exceeding 45% while incorporating online reprocessing capabilities, whereas SMRs provide advantages in modular deployment and intrinsic safety features. FBRs facilitate closed fuel cycles and the transmutation of long‐lived isotopes. Lifecycle emissions consistently remain below 12–20 gCO2e/kWh. Empirical case studies from India, China, and the United States substantiate this field's technical readiness and regulatory progress. Advanced fuel compositions and reactor systems offer a plausible trajectory toward sustainable nuclear energy. The achievement of this potential is contingent upon the evolution of contemporary regulatory frameworks, active public engagement, and adequate financial mechanisms. Integrating technology, policy, and public trust is essential to making nuclear energy a key pillar of global decarbonization.

Micro- and nanoplastics (MNPs) have become enduring pollutants in aquatic ecosystems, posing escalating threats to biological communities and human well-being and necessitating advanced separation methodologies. Functional membranes and engineered adsorbents with customized surface chemistry, wettability, and porosity have demonstrated significant potential for extracting MNPs from potable water, sewage, and industrial discharges. This review meticulously scrutinizes recent progress in MNP-focused separation materials and system architectures, accentuating the influence of particle size, polymeric composition, environmental degradation, and biofilm interactions on removal efficacy. Polymeric, ceramic, and hybrid membranes, in conjunction with mineral- and bio-derived adsorbents, are evaluated concerning antifouling capacity, regeneration potential, and compatibility with concurrent contaminant removal. Emerging process configurations, including membrane bioreactors, dynamic filtration systems, and hybrid adsorption–oxidation methodologies, are examined with respect to hydraulic performance, fouling progression, and energy requirements. The review underscores that aggregation or immobilization should not be misconstrued as genuine eradication, emphasizing the necessity for enduring containment strategies. Principal challenges, such as material deterioration, secondary microplastic formation, analytical ambiguity, and limited techno-economic evaluations, are discussed. Aligned with Sustainable Development Goals 6 and 12, this work proposes an integrated framework amalgamating advanced materials, optimized system architecture, and digital oversight for sustainable MNP abatement.

Thin-film spectral selective absorber (SSA) coatings applied to absorber fins play a critical role in maximising thermal energy harvesting in solar flat plate collectors (FPSC) by efficiently utilising the full solar radiation spectrum. Though the effects of tandem spectral selective absorber (SSA) coatings are profound in solar energy harvesting techniques, the nanoparticle-enhanced matte black paints emerge as a simple, cost-effective, and environmentally benign alternative, offering ease of fabrication and superior adaptability to complex surface morphologies. The nano coating comprising Fe3O4 and graphene nanoparticles in black matte paint on the absorber tube of PTSC substantially reduced the heat loss coefficient (UL) markedly from 228.18 W/m2K to 46.12 W/m2K.Whereas Fe3O4 extended the thermal conductivity of black paint by 0.031 W/mK. The incorporation of metal oxide nanoparticles in coatings is extensively employed to impart hydrophilic or hydrophobic and photocatalytic qualities to photovoltaic panel surfaces, hence enhancing durability in severe environments while providing economic advantages. The graphene nano black paint can retain absorptivity of greater than 0.9 in the wavelength range from 200 nm to 1500 nm, which is 6% higher than conventional black paint. Despite these advantages, quantitative studies addressing energy and exergy enhancement, system size reduction, and associated CO2 emission mitigation remain scarce. Furthermore, the potential of integrating active enhancement strategies-such as mechanical vibration and robotic wiper mechanisms-to further improve nanocoating effectiveness is identified as an emerging research direction. Statement of Novelty This study delivers a comprehensive critical review of nano-enabled spectral selective absorber (SSA) coatings and nano-enhanced matte black paints for solar thermal applications, integrating coating chemistry, surface morphology, heat transfer, and energy-exergy performance. The work uniquely positions nano-enhanced black paints as a scalable alternative to conventional SSA coatings and proposes future pathways involving nanoporous structures, diffusion barriers, and green-synthesized nanoparticles. Statement of Industrial Relevance. This study provides industry-relevant guidance for designing cost-effective, high-performance solar thermal systems by comparing advanced SSA coatings with scalable nano-enhanced matte black paints. It addresses practical challenges in coating complex and extended absorber surfaces, system optimisation under pressuredrop constraints, and pumping power penalties. The findings support collector size reduction, improved thermal efficiency, and reduced operational energy demand. Emphasis on green-synthesised nanoparticles aligns with sustainability and regulatory requirements, offering a viable pathway for large-scale manufacturing, retrofitting, and commercialisation of durable, environmentally benign solar thermal technologies.

This study examines the conversion of orange peel waste into low-emission biodiesel enhanced with zinc oxide (ZnO) nanoparticles. Turning agricultural residues into sustainable fuels cuts environmental pollution and reduces reliance on fossil diesel. Orange peel oil was extracted by solvent-assisted distillation and converted to biodiesel via transesterification. ZnO nanoparticles were added to the biodiesel at 25 and 50 ppm by ultrasonic dispersion. The blends were tested in a single-cylinder diesel engine. Emissions of carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides (NOx), and smoke opacity were analyzed. Thermal efficiency was also measured to assess environmental impact and energy performance. The biodiesel with 50 ppm ZnO (B100 + ZnO 50 ppm) achieved a 6.06% higher brake thermal efficiency (BTE) than neat biodiesel. It also produced substantial emission reductions: CO decreased by 61.7%, HC by 38.1%, and smoke by 42.3% compared with diesel. However, NOx emissions increased moderately by 14.7%, likely due to enhanced combustion efficiency and higher peak oxidation temperatures from ZnO nanoparticles. This nano-enhanced orange peel biodiesel shows strong environmental potential as a low-emission, renewable diesel substitute. It supports waste valorization and pollution abatement. This approach promotes circular bioeconomy principles by transforming agro-industrial residues into eco-efficient energy carriers compatible with current diesel infrastructure.

Ti-6Al-4V alloy is extensively used for biomedical and dental implant applications due to its outstanding biocompatibility, corrosion resistance and favorable mechanical strength. However, its limited wear resistance, and long-term stability necessitate further improvement. This study investigates the effects of TiO2, yttriastabilized zirconia (YSZ), hydroxyapatite (HAp), and chitosan nanoparticles on the densification, microstructural features and mechanical/tribological behaviour of Ti-6Al-4V matrix nanocomposites. The nanocomposites were fabricated using powder metallurgy route followed by conventional sintering at 1500 degrees C in a hydrogen atmosphere. Reinforcements were incorporated at 5, 10 and 20 wt % concentrations. FESEM and XRD analyses confirmed a homogeneous dispersion and strong interfacial bonding between nanoparticles and Ti matrix. The addition of reinforcements significantly enhanced densification behaviour, hardness, compressive strength, impact strength, and wear resistance compared with pure Ti-6Al-4V alloy. Nanocomposites containing 5 wt % reinforcement exhibited superior densification with reduced internal cracks and voids, indicating improved structural integrity. Increasing reinforcement content further contributed to superior mechanical and tribological performances. Based on the observed microstructural, mechanical, and tribological characteristics, and biomechanical requirements reported in the literature for stable dental implant materials, Ti+10 wt % TiO2, Ti+ 10 wt % YSZ, and Ti+ 10 wt % chitosan nanocomposites emerged as the most promising candidates for future dental implant applications. The study highlights the potential of nanoparticle-reinforced Ti-6Al-4V nanocomposites as advanced, durable and high-performance dental implant materials.

Global energy consumption continues its upward trajectory, pushing annual carbon dioxide (CO2) emissions beyond 36 Gt and underscoring the need for effective carbon mitigation strategies. CO2 valorization has emerged as a promising paradigm to reduce emissions while generating valuable fuels, chemicals, and materials, thereby facilitating the transition toward a circular carbon economy. This review amalgamates recent advancements across electrochemical, photochemical, biological, and thermochemical pathways, with particular emphasis on catalytic innovations, energy efficiency, reaction selectivity, and product yields. Electrochemical systems now report conversion efficiencies approaching 90%, whilst enhancements in photocatalysts and engineered biocatalytic platforms indicate burgeoning potential despite ongoing challenges in scalability, durability, and operational expenditures. A comparative techno-economic evaluation is presented for CO2-derived fuels, polymers, and specialty chemicals, covering production costs, returns on investment, and payback periods. Empirical case studies from industrial and pilot-scale projects illuminate both successful implementations and enduring deployment obstacles. Environmental performance is assessed through life-cycle analysis (LCA), demonstrating that renewable-energy-integrated CO2 conversion pathways achieve substantially lower carbon footprints than conventional production methodologies. Finally, an international policy examination including carbon pricing mechanisms, tax incentives, and targeted subsidies highlights the indispensable role of regulatory support in expediting industrial adoption. Collectively, this review delineates critical technological, economic, and policy facilitators required to propel CO2 valorization toward large-scale, sustainable implementation.

Abstract Biomass and organic solid waste are increasingly recognized as promising renewable feedstocks capable of supporting a clean, carbon‐neutral energy infrastructure. Efficient conversion of these resources into high‐value secondary energy carriers is therefore essential to meet escalating global energy demands. Among these carriers, hydrogen stands out due to its high gravimetric energy density, exceptional purity, conversion flexibility, and compatibility with multiple end‐use technologies. This review provides a comprehensive assessment of emerging pathways and technological advances for producing hydrogen from biomass and organic solid waste. Recent progress in both thermochemical and biological conversion routes is critically evaluated. Thermochemical pathways—including gasification, pyrolysis, steam reforming, partial oxidation, and thermochemical cycles—are examined with respect to reaction mechanisms, process efficiency, and integration potential. Likewise, biological routes encompassing enzymatic hydrolysis, microbial and dark fermentation, and direct and indirect biophotolysis are analyzed for their scalability, yield limitations, and system optimization strategies. Key challenges related to feedstock variability, catalyst design, process intensification, and environmental impacts are discussed to illuminate the practical viability of hydrogen production within a bio‐based circular economy. The review highlights future research directions essential for advancing biomass‐ and waste‐derived hydrogen as a cornerstone of a sustainable hydrogen economy.

The integration of waste biodiesel, metal oxide nanocatalysts, and gaseous dual-fuel combustion enhances compression ignition (CI) engine performance and reduces emissions. This investigation has been carried out on soapstock biodiesel (SB) produced from soapstock (waste material of vegetable oil processing), enhanced with a hybrid nanocatalyst of graphene oxide (GO) with titanium dioxide (TiO2) nanoparticles at 50 parts per million (ppm). Producer gas (PG), a fuel gas mixture produced through biomass gasification, is also used to facilitate combustion at 4 and 8 lpm in a CI engine. The nano-enabled fuel blend, B50 (50 SB + 50 D) containing GO/TiO2 at 50 ppm augmented with PG at 8 lpm also showed superior combustion, performance and emission results. Maximum cylinder pressure increased by 5.6% over diesel, while the heat release rate (HRR) rose by 9.75%, indicating enhanced combustion. The brake thermal efficiency (BTE), representing the capacity of utilizing the fuel energy to produce the mechanical work in the engine, increased by 6.45% and the brake specific energy consumption (BSEC), which is the energy consumption per unit brake power, decreased by 2.73%, indicating better fuel utilization. The analysis of emissions revealed decreases of 41.7% in carbon monoxide (CO), 29.8% in hydrocarbons (HC), and 20.9% in smoke opacity (the amount of soot in the exhaust). Nitrogen oxide (NOx) emission was reduced by 6.67% with the nano-assisted dual-fuel operation. Results indicate that integrating nanocatalysts and producer gas with waste-based biodiesel enhances CI engine performance, reduces emissions, and improves sustainability.

The growing demand for carbon-neutral fuels has driven increased research into hydrogen (H-2)-assisted biodiesel combustion. Engine performance, combustion, and emissions were studied using algae biodiesel blends with H-2 enrichment at 3 and 6 LPM. A graph neural network (GNN) model was also developed to link experimental dual-fuel data with engine behavior predictions. Experiments of six biodiesel blend ratios and two H-2 flow rates were performed at five different loads (0-100%), evaluating performance, combustion, and emissions. Due to the lower calorific value of the fuel, the brake thermal efficiency (BTE) reduced by 6.1% with a higher biodiesel mixture, and 6 LPM H-2 enhanced the engine performance by 3.7% and compensated for the thermal energy loss. The H-2 enrichment enhanced peak pressure and heat release rate (HRR) by 6-6.4%, compensating for losses from biodiesel usage. Overall, nitrogen oxides (NOx) emissions increased by 23.1% with B100 and 3.6% for 6 LPM H-2 addition. Hydrocarbons (HC) were reduced by 87.5%, carbon monoxide (CO) by 28.8%, and the total amount of smoke decreased by 27.1% with the B100 + 6 LPM H-2 condition. A 90-node heterogeneous GNN using 38 physics-informed features achieved R-2 >0.95 and RMSE <5% for five simultaneous outputs, effectively capturing nonlinear interactions between hydrogen and biodiesel. Overall, H-2 enhances the performance and clean-burning potential of algae biodiesel, significantly reducing key pollutants while causing a modest increase in NOx. The developed GNN framework provides an efficient predictive tool for optimizing H-2 biofuel dual-fuel engines and supports the advancement of low-carbon combustion technologies.

Water hyacinth (WH, Eichhornia crassipes) is a highly invasive aquatic macrophyte that degrades freshwater ecosystems. Yet it constitutes an abundant, low-cost lignocellulosic resource that can be valorized to produce renewable hydrogen (H2) within circular bioenergy systems. This review critically synthesizes water-hyacinthspecific evidence for thermochemical (pyrolysis, gasification, catalytic upgrading/reforming) and biological (dark and photo-fermentation) pathways, with particular attention to reporting basis, moisture management, and integration with invasive-biomass control and wastewater remediation. Reported WH H2 yields vary widely (typically 10-22 mmol H2/g dry WH depending on catalyst, reactor, and moisture). Thermochemical studies demonstrate strong configuration dependence across FeCl3-assisted pyrolysis, air gasification, and microwave chemical-looping systems. In contrast, biological routes benefit from two-stage dark-photo fermentation but remain constrained by inhibitors, reactor hydrodynamics, and light delivery. Because studies employ noncomparable units (vol%, mL, mmol g- 1 VS, Nm3 kg- 1), this review standardizes metrics where feasible and flags unsupported conversions. The techno-economic estimates presented in this review are scenario-based rather than universal and depend strongly on drying energy, transport distance, and catalyst lifetime. The review evaluates limited pilot evidence, identifies verification gaps (scale, operating period, feed moisture, gas quality, cost breakdown), and outlines research priorities on hybrid solar-waste-heat drying, low-inhibitor pretreatment, tar-resilient modular reactors, and policy mechanisms that recognize invasive-biomass removal and verified coproduct benefits (biochar/digestate).

Abstract Industrialization, urbanization, and consumer activity have sharply increased agricultural, plastic, industrial, municipal, and electronic waste, creating major environmental and resource management challenges. Converting waste into functional nanomaterials provides a sustainable path for resource recovery and fosters the development of circular‐economy technologies. This review critically analyzes links between structure, properties, and performance of waste‐derived nanomaterials for energy storage and water remediation. It clarifies how waste chemistry, synthesis methods, and nanostructure features influence electrochemical and environmental outcomes. Synthesis strategies, including pyrolysis, hydrothermal processing, chemical activation, sol–gel techniques, and green methods, are reviewed with a focus on their impact on porosity, surface area, conductivity, and catalytic activity. Waste‐derived carbon nanomaterials, metal oxides, silica structures, and hybrid nanocomposites show strong promise as electrode materials for supercapacitors, lithium‐ion batteries, sodium‐ion batteries, and metal–air batteries, as well as achieving efficiency in pollutant removal and water purification. Hierarchical porosity, surface functional groups, and hybrid architectures are shown to enhance charge storage, ion transport, catalytic reactions, and adsorption in these systems. The review examines sustainability, the benefits of the circular economy, techno‐economic barriers, scalability concerns, and environmental impacts. Finally, it clarifies future directions in AI‐assisted design, process optimization, scalable synthesis, and industrial implementation, supporting practical adoption of waste‐derived nanomaterials for sustainable energy and environmental solutions.

ABSTRACT Waste‐derived biodiesel offers a sustainable alternative to diesel fuel but faces challenges in combustion and emissions. This study evaluates a CRDI diesel engine fueled with B50 duck waste fat biodiesel blended with 50 ppm Al(NO 3 ) 3 nanoparticles under varying injection timings (21–25°CA bTDC) and injection pressures (500–600 bar). A long short‐term memory (LSTM) model was developed to predict performance and emissions. Under optimal conditions (25°CA bTDC and 600 bar), brake thermal efficiency (BTE) reached 30.85%, whereas smoke, hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx) emissions decreased by 17.04%, 20.14%, 27.17%, and 16.8%, respectively, compared with diesel. The LSTM model achieved R 2 values above 0.92 for all outputs. The novelty lies in combining Al(NO 3 ) 3 nano‐additives, injection optimization, and LSTM modeling to improve the combustion and emission characteristics of waste‐fat biodiesel in CRDI engines.

A sustainable, low-carbon combustion strategy is proposed that integrates fish-waste biodiesel, nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs), and ammonia (NH3) fumigation to enhance combustion efficiency and reduce emissions in diesel engines. Specifically, the study investigates nanocatalytic and hydrogen (H2) assisted mechanisms for NH3 decomposition, aiming to improve efficiency and reduce pollutant emissions. To test these mechanisms, experiments were conducted using a single-cylinder, four-stroke diesel engine operating at 1500 rpm. The test fuels included diesel, biodiesel (B100), and B100 blended with 40, 80, and 120 ppm N-MWCNTs. Additionally, all fuels were evaluated under constant NH3 fumigation at 5 LPM. At maximum load, results showed that the optimized tri-fuel blend (B100 + N-MWCNTs 120 ppm + NH3 5 LPM) achieved a 7.8% higher maximum cylinder pressure and a 13.5% higher heat release rate (HRR) than diesel, and 12.5% and 22.3% higher than B100, respectively. Furthermore, brake thermal efficiency (BTE) increased by 15.4% compared to diesel and 29.2% compared to B100, while brake specific energy consumption (BSEC) decreased by 22.3% and 35.6%, respectively. With respect to emissions, reductions in carbon monoxide (CO), hydrocarbons (HC), and smoke opacity were observed: 38%, 12%, and 37% lower than with diesel, and 30.6%, 5%, and 28.6% lower than with B100, respectively. However, oxides of nitrogen (NOx) emissions increased by 31.1% over diesel and 22.7% over B100. Collectively, nanocatalytic oxidation by N-MWCNTs and H2 enrichment from NH3 decomposition improved performance and reduced emissions. These findings indicate that the tri-fuel system represents a scalable waste-to-energy pathway consistent with the Sustainable Development Goals.

This study develops a clean, high-efficiency combustion strategy for agricultural diesel engines by integrating spent coffee ground biodiesel (SCGB) with graphene oxide-zinc oxide (GO@ZnO) core-shell nanoadditives. A Physics-Informed Thermodynamic Graph Neural Network (Thermo-GNN) is introduced to predict performance and emissions behavior using sparse experimental data. SCGB was produced via acid-base transesterification, blended with diesel (B25-B100), and doped with 50 and 100 ppm GO@ZnO nanoparticles. Experiments were performed on a single-cylinder diesel engine at 1500 rpm. Thermo-GNN was trained on 15 full-load pressure traces using nine physics-based constraints, including closed-cycle energy conservation, ideal-gas consistency, ignition-delay regularization, and an oxygen-donation constraint. Accuracy was tested on interpolation and extrapolation regimes. GO@ZnO improved combustion, raising peak pressure by 8.9% and peak heat-release rate by 45% versus diesel. The highest brake thermal efficiency (BTE) was 33.5% (7.7% above diesel), and brake specific fuel consumption (BSFC) decreased by 7.1%. Emissions dropped by 27.5% for carbon monoxide, 30.8% for hydrocarbons, 17.1% for nitrogen oxides (NOx), and 65% for smoke with the optimal nanofuel blend. Thermo-GNN accurately reconstructed pressure traces (R-2 > 0.9987) and predicted BTE, BSFC, NOx, and smoke, with mean absolute percentage errors of 2.3%, 2.7%, 7.1%, and 12.6%, respectively, even under double extrapolation. Attention and latent-variable analyses confirmed mechanistic learning of premixed-phase catalytic activity and lattice-oxygen donation. The combined SCGB-GO@ZnO fuel pathway and the Thermo-GNN framework provide a scalable, physically interpretable foundation for deploying digital twins in existing diesel engines.

This study experimentally investigated the performance, combustion, and emission characteristics of a compression ignition engine (CI) fueled with tamanu methyl ester biodiesel blended at 20% with diesel (TMB20) and enhanced with graphene oxide (GPO) nanoadditives. The tested fuel variants included TMB20, TMB20 + GPO15 ppm, TMB20 + GPO30 ppm, TMB20 + GPO45 ppm, and TMB20 + GPO60 ppm, which were evaluated against diesel. The results revealed that GPO integration significantly improved engine performance, with the TMB20 + GPO60 ppm blend exhibiting the highest brake thermal efficiency and lowest brake-specific fuel consumption. Enhanced atomization, a higher calorific value, and a shorter ignition delay contribute to improved combustion efficiency. Emission analysis indicated notable reductions in carbon monoxide (29.68%), unburned hydrocarbons (50.54%), and smoke opacity (44.92%) compared to diesel. While most blends showed an increase in nitrogen oxide (NOx) emissions, the TMB20 + GPO60 ppm blend achieved a 9.75% reduction in NOx emissions compared to diesel. Moreover, the peak cylinder pressure and heat release rate increased with increasing GPO concentrations, confirming the superior combustion characteristics of GPO. In general, the integration of GPO nanoadditives with tamanu biodiesel substantially enhanced engine performance and emission behavior, underscoring its potential as a sustainable and efficient alternative fuel for CIs used in automobile and marine applications.

The sustainable use of biomass resources is the key to developing low carbon bioenergy systems and decreasing reliance on fossil-based fuels. In the domain of thermochemical routes, biomass gasification and pyrolysis are considered the most promising approaches to achieve hydrogen (H2)-rich syngas conversion of lignocellulosic feedstock while producing energy recovery with added value and resource utilization with carbon efficiency. A comprehensive review on biomass-based H2-rich syngas production in terms of feedstock properties, reactors, catalytic reforming route, thermodynamics, techno-economic and life-cycle sustainability is presented. The impact of the lignocellulosic content, moisture, ash chemistry and pretreatment on H2 production and syngas quality is critically reviewed. The trade-offs in terms of carbon conversion, tar control, and scalability in bioenergy systems are informed through comparative assessment of fixed-bed, fluidized-bed, entrained-flow, dualstage, and plasma gasifiers. Various catalytic strategies such as Ni-based catalysts, the addition of alkali, transition metal oxides, and materials derived from waste are discussed regarding the potential to improve H2 selectivity and stability of the process. Techno-economic and life cycle studies validate that biomass gasification, coupled with carbon capture and heat recovery, can provide competitive H2 cost under low/negative carbon intensity considering sustainable supply of biomass. By combining feedstock engineering, reactor design, and environmental metrics, we provide insight into the role of biomass-derived H2 in a circular bioenergy future and identify opportunities for sustainable, scalable, resource-efficient biohydrogen production.

Biodiesel production from low-cost feedstocks remains constrained by catalyst costs, sensitivity to free fatty acids, soap formation, separation difficulties, and inconsistent catalyst reusability. This review critically evaluates waste-derived nanocatalysts for converting waste cooking oil (WCO) and non-edible seed oils into biodiesel, with emphasis on calcium-rich wastes, biomass ash, biochar-supported catalysts, green-synthesized metal oxides, magnetic composites, and bifunctional acid-base systems. Reported catalytic activity generally follows the order: engineered CaO-rich shell/eggshell catalysts and mixed CaO composites > green-synthesized transition-metal oxides > biomass ash and biochar-supported systems, although performance strongly depends on feedstock acidity, catalyst basicity, crystallite size, pore accessibility, leaching resistance, and reactor mode. Recent studies on non-edible oils, including Cannabis sativa, Diospyros malabarica, Carthamus lanatus, Ipomoea carnea, Quercus incana, Mallotus philippensis, Caesalpinia crista, and Phyllanthus maderaspatensis, show biodiesel yields of approximately 94–98% under optimized conditions using WO₃, CdO₂, Bi₂O₃, Al₂O₃, Cr₂O₃, and related green nanocatalysts. The review further integrates bibliometric trends, machine-learning-assisted optimization, kinetic descriptors, activation-energy analysis, cost estimation, catalyst deactivation, barriers to continuous-flow scale-up, and end-of-life catalyst management. The analysis shows that future progress depends less on reporting the maximum single-cycle yield and more on standardized benchmarking of catalytic activity, free fatty acid (FFA) tolerance, reusability, regeneration, pressure-drop behavior, production cost, and life-cycle sustainability.

This work examined the combined effects of waste cooking oil biodiesel (WCOB), NiFe2O4 nanocatalysts, and hydrogen (H2) enrichment on in-cylinder processes, engine performance, and emissions of a diesel engine. To accurately represent the physical processes and to derive thermodynamically consistent predictions, a physics-encoded multi-task machine learning (PE-MTMML) model was developed. Tests were carried out on a single-cylinder, four-stroke diesel engine at 1500 rpm. The engine was operated on blends of diesel, WCOB, and NiFe2O4 (50-150 ppm) with the addition of H2 at 5 LPM. The analysis of combustion was done based on the measurement of in-cylinder pressure with respect to the crank angle from which peak pressure and heat release rate (HRR) were derived using a single-zone model. Performance parameters were obtained at various loads through the full load range. The PE-MTMML model incorporated not only the thermodynamic reciprocity but also catalytic oxidation trends and root-sum-square (RSS) uncertainty constraints. At full load, the NiFe2O4 nanoparticles improved catalytic oxidation and premixed combustion, thus, the peak pressure rose by 7.8% at most, and HRR by 14% compared to diesel. The ensemble of WCOB + NiFe2O4 150 ppm + H2 led to an increase in brake thermal efficiency (BTE) of 29.2% and a decrease in brake-specific energy consumption (BSEC) of 22.3% in comparison with diesel. Inspection of emissions revealed that the smoke opacity was lessened by 10.9%, carbon monoxide (CO) by 20%, and hydrocarbons (HC) by 25%, while nitrogen oxides (NOx) were elevated by 7.5% relative to diesel. The PE-MTMML model had excellent prediction capabilities (mean R2 = 0.9993) and at the same time adhered to thermodynamic constraints. The synergistic effect of NiFe2O4 nanocatalysis and H2 enrichment makes WCOB both a high-efficiency and a low-pollution fuel. By allowing for optimization with minimal experimental input, the PE-MTMML scheme acts as a trustworthy digital twin, supporting circular-economy goals and the transition to sustainable, carbon-neutral diesel engines.

Decarbonizing industrial heat, buildings, and data centers at scale need thermal energy storage (TES) that is compact, reliable, and easy to use. Phase change material (PCM)-based TES stores and releases heat at nearly constant temperatures in a small space. But its adoption is slowed by slow heat transfer, material degradation over repeated use, and a patchwork approach to combining materials, systems, and controls. This review provides an overview of PCM TES, including how materials are manufactured, how they degrade, how they fit into larger systems, new ways to control them, and their cost-effectiveness. We look at different types of PCMs, how they are packaged, how they age, how to predict their lifespans, and new control methods such as model-based control and digital systems. The main result is a guide connecting PCM properties and how they break down to how the system is set up, how smart controls work, and what it costs to store energy, filling a key gap in current research. Results show that reliable design and advanced controls improve response, allow more than 10,000 cycles, and cut stored energy cost below 0.05 /kWh with frequent use. Examples from factories, buildings, and data centers show PCM TES cuts carbon dioxide (CO2) emissions and helps balance the electricity grid. The review concludes with practical advice and research tips to accelerate the rollout of reliable, smart, and affordable PCM TES for low-carbon energy use.

This study advances the concept of waste-to-hydrogen (WtH₂) hubs as integrated industrial ecosystems that jointly address waste valorization and low-carbon hydrogen supply for hard-to-abate sectors. Conversion pathways—thermochemical, biochemical, hydrothermal, and electro/photo-assisted—are critically compared using harmonized techno-economic and life-cycle metrics to enhance cross-study consistency. Thermochemical routes show the highest readiness, achieving 40–80 g·kg−1 feedstock and 3–6 USD·kg−1 H₂, while biochemical and electro-assisted pathways enable superior handling of wet wastes and renewable coupling. Results reveal that feedstock logistics, purification efficiency, electricity carbon intensity, and industrial co-location outweigh pathway selection in determining viability, with life-cycle outcomes highly sensitive to grid conditions. Digital twins, model predictive control, and federated analytics emerge as pivotal for ensuring purity, flexibility, and resilience. A TRL-informed roadmap identifies thermochemical and hybrid hubs, co-located with demand and supported by robust MRV frameworks, as the most bankable near-term deployment pathway.