The use of bio-based materials in lithium-ion separation technologies has grown significantly in recent years due to the availability, tunable properties, and potential to reduce dependence on fossil-derived resources. However, the literature demonstrates that bio-based material are applied in fundamentally different ways, and their functional roles are often not clearly delineated. Therefore, this review aimed to introduce a conceptual framework that classifies lithium-ion separation systems according to the functional role of bio-based components. Three principal categories are identified, namely Bio-based Structural Matrix (BSM), Bio-based Active Chelators (BAC), and Bio-based Hybrid Systems (BHS). BSM systems primarily employ biomaterial as structural supports for external chelating agents, including inorganic ion sieves (lithium manganese oxides and titanium oxides) or organic chelators (crown ethers and commercial extractants). The systems generally provide high adsorption capacity and selectivity suitable for highly competitive lithium sources such as seawater and salt-lake brines. In contrast, BAC exploit either the intrinsic functional groups of biomaterial or chemically introduced groups as active lithium-binding sites. The systems offer simpler synthesis routes and stronger sustainability credentials, although the adsorption performance varies considerably depending on the modification strategy. Hybrid systems aim to integrate the advantages of both approaches by enabling biomaterial to function simultaneously as structural matrices and active chelators. This framework enhances understanding of the diverse roles of bio-based material in lithium separation technologies while also providing guidance for the rational design of more efficient, economical, and sustainable lithium recovery systems.
Rice husk (RH), an abundant and low-cost agricultural by-product in rice-producing countries, is commonly used as a fuel in boilers, generating rice husk ash (RHA) as a combustion by-product. Given their advantageous chemical compositions and surface characteristics, RH and RHA hold significant potential as precursors for synthesizing adsorbents aimed at water and wastewater remediation. This review provides a comprehensive overview of the synthetic pathways for converting RH and RHA into functional adsorbents including biochar, activated carbon, zeolites, and silica-based derivatives, alongside their applications in the remediation of various aquatic contaminants. The synthesis methods and characterization techniques for RH- and RHA-derived adsorbents are discussed, together with a critical evaluation of adsorption mechanisms, including isotherms and kinetics. Key factors governing adsorption performance toward heavy metals, dyes, and organic contaminants are systematically examined based on recent studies. Additionally, issues related to the regeneration and reusability of these adsorbents are addressed. The current literature collectively supports the promising role of RH and RHA as sustainable feedstocks for the development of low-cost adsorbents in aquatic pollution remediation.
Using food waste as an adsorbent is a choice for wastewater treatment by the adsorption method to achieve sustainable resource and waste disposal and management. This study aimed to synthesize methylene blue dye (MB) adsorbents from quail eggshells with and without zinc oxide (ZnO), which were quail eggshell beads (QB) and quail eggshell modified with ZnO beads (QZB), and to characterize them using XRD, FESEM-FIB, EDS, FTIR, and pHpzc techniques. Batch experiments were used for investigating their MB removal performances, and their reusable abilities were examined by desorption experiments. Various isotherm and kinetic models were used for determining their adsorption patterns and mechanisms. Their temperature effects were explored by thermodynamic studies. QB and QZB were semi-crystalline structures and showed specific peaks of CaCO3. Moreover, QZB also detected specific peaks of ZnO. They had a sphere-shaped structure, and their surfaces were uneven and coarse with porous structures. Their main chemical compositions were C, O, Ca, Cl, and Na, while Zn was only found in QZB. The functional groups of O–H, C=O, C–O, and Ca–O were found in QB and QZB, while Zn–O was only detected in QZB. The pHpzc values of QB and QZB were 6.51 and 6.62. QZB demonstrated higher performance on MB adsorption in terms of MB removal efficiencies (%) and adsorption capacity (qe) at 86.82 %±3.04 and 51.97±2.97 mg/g than QB at 79.92±2.36% and 29.97±2.14 mg/g by approximately 7% and 22 mg/g, so ZnO could improve the material's ability, especially increasing qe by more than 1.7 times. The desorption experiments could confirm their reusable abilities for more than three cycles with high MB removal efficiencies of more than 71%. Freundlich and pseudo-second-order kinetic models were good at explaining their adsorption patterns and mechanisms related to multilayer adsorption on heterogeneous surfaces and a chemisorption process. Moreover, their MB adsorption was an exothermic process. Therefore, QZB might be a good choice for MB adsorption in further wastewater treatment.
The valorization of cocoa pod husks (CPH) into high-value biopolymers supports a circular bioeconomy; however, sustainable processes for recovering high-quality low-methoxyl (LM) pectin remain limited. Although ultrasound-assisted extraction (UAE) has been explored for pectin recovery, the integration of tartaric acid with probe-type UAE under ambient conditions has not been reported for CPH pectin recovery. This study aimed to develop and optimize an ambient tartaric acid-assisted UAE process for pectin extraction from CPH using response surface methodology (RSM), followed by physicochemical characterization and evaluation of the film-forming properties. The optimum conditions (pH 2.1, amplitude 48%, and extraction time 22 min) were found to yield 14.41% pectin, closely matching the predicted value and confirming the model adequacy. The extracted pectin exhibited low-methoxyl characteristics, with a degree of esterification of 25.07%, a methoxyl content of 2.07%, and a galacturonic acid content of 85.66%. It also exhibited a high lightness value (L* = 84.00), indicating that tartaric acid-assisted extraction produced light-colored pectin. FTIR and TGA–DSC analyses confirmed the characteristic structure and thermal stability of the extracted pectin, while SEM observations revealed substantial disruption of plant cell walls following ultrasound treatment. Importantly, the recovered pectin formed continuous and homogeneous films with greater flexibility than commercial LM pectin, although its tensile strength remained lower. This study establishes ambient-tartaric acid-assisted UAE as a mild and potentially greener route for valorizing CPH waste into value-added LM pectin. The process offers a strategy for waste minimization, reduces reliance on high-temperature processing, and supports biobased packaging applications.
The need to develop cost-effective and green adsorbents for dye removal from water is an area of concern for water treatment. In this paper, the green adsorbent Ceratonia siliqua leaves (CSL) was used to remove Congo Red (CR) dye. A series of physicochemical analyses were carried out to characterize the green adsorbent. First, the effects of various operational factors on the CR removal efficiency were investigated. Subsequently, the process was optimized using the Box-Behnken design (BBD) method. The optimal values for the parameters were found to be 2.55 mg for the amount of adsorbent used, a pH of 3.58, and a contact time of 45.13 min. Using these optimal values, the removal capacity of the adsorbent for CR dye was predicted to be 614.83 mg/g. However, the actual removal capacity of the adsorbent for CR dye was found to be 610.31 mg/g or 99.80% of the removal efficiency. The obtained results confirmed the effective adsorption performance of CSL toward CR removal, highlighting its potential as a low-cost and sustainable biosorbent for wastewater treatment applications. The adsorption kinetics and equilibrium data were best described by the pseudo-second-order and Langmuir models, respectively. The thermodynamic study showed that adsorption is spontaneous and endothermic. RSM and ANN models showed excellent predictive performance, with R2 values of 0.997 and 0.990, respectively. These findings demonstrate how statistical and machine learning methods can work in tandem. This study showed CSL as a promising adsorbent in the removal of dyes in water treatment, being eco-friendly and affordable.
The thermal-hydraulic performance of perforated pin-fin arrays is critically influenced by fin geometry, perforation configuration, and flow conditions. This study presents an integrated computational fluid dynamics (CFD) and machine learning framework to systematically investigate and predict the heat transfer and pressure drop characteristics of circular, square, and diamond-shaped pin fins with single, double, and triple perforations. High-fidelity CFD simulations provided detailed insights into flow structures, turbulence intensity, and convective heat transfer mechanisms, revealing that fin geometry strongly governs wake development and turbulence production, while perforations effectively moderate pressure losses. The resulting CFD dataset was employed to train Extreme Gradient Boosting (XGBoost) regression models, which accurately predicted pressure drop and heat transfer coefficients, achieving coefficients of determination exceeding 0.93 and 0.99, respectively. The proposed hybrid CFD-AI methodology enables rapid and reliable performance evaluation, offering a powerful tool for the design optimization of perforated pin-fin heat sinks in advanced thermal management applications.
The growing demand for cobalt in battery and alloy production has intensified the need for efficient and sustainable recovery methods from complex refinery streams. Conventionally saponified Cyanex 272 systems require stringent pH control and continuous ammonia dosing, creating operational and environmental challenges. To address these limitations, this study introduces a novel approach using amine-modified Cyanex 272 for selective cobalt extraction. Unlike previous work focused on saponification, this research demonstrates the first application of butyl- and hexyl-modified Cyanex 272 ([C4H9NH2][Cyanex 272] and [C6H13NH2][Cyanex 272]) in real refinery liquors containing 1.9 g/L Ni, 0.53 g/L Co, and 436 g/L (NH₄)₂SO₄ at pH 6.5. FT-IR and NMR analyses confirmed successful modification of the extractants. Results revealed that the butylamine-modified system achieved near-complete cobalt extraction (up to 99.9%) at concentrations as low as 1.5% v/v, while limiting nickel co-extraction to below 6%, even under unfavorable Ni/Co ratios. The modified extractants maintained stable performance across a wide pH and temperature range, reducing ammonia dependency and improving phase stability. Thermodynamic analysis indicated that cobalt uptake is endothermic and entropy-driven, explaining enhanced selectivity at elevated temperatures. Stripping studies further confirmed efficient cobalt recovery (>99%), a novel, environmentally responsible solution for sustainable cobalt extraction from complex refinery streams.
Convection from the environment and energy generation in porous envelopes are significant for the thermal productivity of tiny heat transfer devices and solar thermal systems. Hybrid nanofluids have better heat transfer than regular fluids. The goal of this study is to quantitatively explore the effects of fluid layer placement on entropy formation and convection heat transfer in nature in a triangle-shaped partitioned chamber filled with a silver magnesium oxide/water hybrid nanofluid layer. The dimensionless governing formulae for laminar and incompressible flow are obtained using the finite component technique. Key parameters examined are the Darcy number (ranging from ten to the power of minus five to ten to the power of minus two), the location of the porous layer (bottom, side, or top region of the triangular partition), and the Rayleigh number (from ten to the power of four to ten to the power of six). The results show that placing the porous layer in the side region increases the average Nusselt number by up to 22% compared to a non-porous configuration, while bottom placement yields a 12% increase. Total entropy generation is reduced by eighteen percent when the porous medium occupies the side region at a Darcy number of ten to the power of minus three. Increasing the Rayleigh number from ten to the power of four to ten to the power of six doubles the thermal entropy generation but reduces the frictional entropy contribution by forty percent. The side porous form has the highest Bejan number, indicating that entropy growth is driven by irreversible heat transmission. The location of the porous media is an important control element for maximizing both heat transmission and thermal efficiency in natural convection flows. The side placement provides the best balance between enhanced Nusselt number and minimized entropy generation. These findings are relevant to advanced thermal management systems, including heat exchangers, solar thermal collectors, HVAC and refrigeration units, thermal energy storage devices, biomedical cooling technologies, nanofluid-based industrial processes, and waste heat recovery systems.
Synthetic dye pollution poses a persistent threat to aquatic ecosystems and human health because of the high stability, toxicity, and resistance of synthetic dyes to conventional wastewater treatments. In this study, mesoporous ZnO(ML) and NiO(ML) photocatalysts were synthesized using a mixed-ligand MOF-derived strategy to engineer their porosity, surface chemistry, and charge-carrier dynamics. The as-prepared materials exhibited large surface areas, controlled pore structures, and modified band positions, which collectively enhanced charge separation and promoted the generation of reactive oxygen species (ROS). The use of mixed-ligand MOF templates produced ZnO(ML) and NiO(ML) with higher porosity and superior photocatalytic performance than those derived from single-ligand MOFs. ZnO(ML) achieved degradation efficiencies of 82.67% for methylene blue (MB) and 96.77% for rhodamine B (RhB) within 90 min, with apparent first-order rate constants of 0.0180 and 0.0336 min−1, respectively, whereas NiO(ML) exhibited rate constants of 0.0109 min−1 for both dyes. Radical scavenging experiments and band-structure analysis further demonstrated distinct ROS hierarchies. Furthermore, the photocatalysts maintained high degradation performance after repeated cycling, demonstrating good stability and reusability. This study provides mechanistic insights into the structure–property relationships of mixed-ligand MOF-derived oxides and guides a rational design pathway for developing robust and sustainable photocatalysts for advanced wastewater remediation.
This study investigates the recycling and valorization of hazardous shaving dust generated from the leather industry into fiber-reinforced biocomposites using natural plant fibers (sugarcane bagasse, areca nut fiber, and groundnut shell) and natural rubber latex (NRL) as a binder. Composite sheets were fabricated via a hand lay-up and coagulation process by varying the shaving dust–NRL ratio and fiber content. The optimal composite formulation, identified by applying MCDM-WSM model, was obtained at 25 wt% leather shaving dust and 75 wt% NRL. Incorporation of natural fibers significantly improved tensile strength (up to 4.7 MPa), flexing index (up to 3.89), and moisture-related properties compared to the unreinforced control composite, achieving performance levels suitable for board-type applications. Thermal analysis revealed enhanced thermal stability of the fiber-reinforced systems, while FTIR and SEM analyses confirmed effective fiber–matrix interactions and uniform morphological features. Short-term exposure to high-humidity conditions and ageing test did not result in any significant deterioration in mechanical performance. Compared with similar composite boards reported in the literature, the developed materials exhibit competitive properties while utilizing waste-derived raw materials. The soil burial biodegradability test revealed a positive degradation behavior of the developed composites throughout the 30-days exposure period. The novelty of this work lies in the integrated valorization of collagen-based leather waste and agricultural residues into functional biocomposites using a latex-based processing route, offering a sustainable, cost-effective pathway for recycling leather industry waste into practical materials, e.g., insole boards, wall coverings, and consumer goods.
Precipitated lignin from black liquor, waste stream of empty fruit bunch (EFB) delignification, was pyrolyzed to yield porous carbon material for H2 storage. Physisorption capacity was governed mainly by pore volume, while trace metals detected on carbon surface increased total H2 uptake through chemisorption. Pyrolyzed lignin releases physisorbed H2 upon mild heating. However, hydrogen bound to metal sites generally requires higher temperatures for desorption during redox cycling. Pyrolyzed lignin obtained at 700°C exhibited the highest porosity with specific surface area (SSA) 416.1 m²/g and thermal-conductivity-detector (TCD) desorption peak area 0.072 a.u. Morphological (SEM-EDS) and elemental (ICP-OES) analyses confirmed the presence of metals on pyrolyzed lignin surface. Density functional theory (DFT) calculation supported this behaviour by identifying the corresponding adsorption energies (Eads) of metal oxide. Physisorption accounted 73.7% of total H2 storage capacity, while the remaining 26.3% was attributed to chemisorption. Low-temperature H2 adsorption-desorption cycling, up to 85°C, confirmed physisorption-dominated release, consistent with low Eads values of DFT calculation for CaO and MgO. Repeated cycling showed 11.3% decrease in H2 storage after the second cycle.
Environmental water contamination by organic pollutants has become a global concern, and conventional treatment methods are often ineffective. In this study, we synthesized TiO2/NaBiS2 nanocomposites on fluorine-doped tin oxide (FTO) substrates to evaluate their efficiency in removing tetracycline via a photoelectrocatalytic (PEC) process. The structural, optical, and electrochemical properties of the samples were analyzed using various techniques. X-ray diffraction confirmed the rutile phase of TiO2, and Scherrer analysis showed that the addition of NaBiS2 did not affect its crystallinity. To optimize reaction conditions, ideal variables for pH, applied voltage, electrolyte, and pollutant concentration were found. Under optimized conditions, the FTO/TiO2/NaBiS2 photoanode degraded 91.4% of tetracycline in 2 hours, which outperforms the 18.9% degradation of FTO/TiO2 by far. The enhanced PEC performance is attributed to the formation of an S-scheme heterojunction, which promotes high-energy surface redox reactions through selective recombination of low-energy charge carriers across the interface. The proposed mechanism is supported by band potential alignment, scavenger tests used to identify active reactive species, and the binding energy shifts observed in X-ray photoelectron spectra recorded under light irradiation, which indicate hole accumulation in TiO2 and electron accumulation in NaBiS2. Additionally, the reaction intermediates were examined by LC-MS analysis, and possible degradation pathways were proposed. Finally, the four consecutive degradation experiments, together with post-cycling FESEM, XRD characterization, and ICP-OES analysis of the treated solution indicate that the photoelectrocatalyst remains relatively stable under the working conditions.
The development of environmentally benign, self-healing anticorrosion coating has become a critical priority following restrictions on chromate-based systems. Halloysite nanotubes (HNTs), naturally occurring aluminosilicate nanocontainers with a hollow tubular morphology, have emerged as highly promising carriers for controlled delivery of corrosion inhibitors. This review critically examines the evolution of halloysite nanotube (HNT)-enabled smart coatings from simple inhibitor encapsulation strategies to advance autonomous healing architectures. The structural characteristics and dual-surface chemistry of HNTs are analyzed in relation to loading efficiency, surface functionalization, and compatibility with polymer matrices. Various modification strategies including silane coupling, polymer grafting, layer-by-layer polyelectrolyte assembly, and metal–inhibitor complex capping are comparatively evaluated for their ability to regulate stimuli-responsive release. The release kinetics of encapsulated inhibitors are discussed using established mathematical models, with emphasis on pH- and chloride-triggered mechanisms relevant to corrosion environments. Electrochemical performance metrics, including impedance evolution and charge-transfer resistance, demonstrate the effectiveness of HNT-based nanocontainers in enabling localized, feedback-controlled inhibitor delivery. The review identifies current limitations related to release synchronization, long-term durability, and scalability, and proposes future research directions toward sustainable, multi-responsive autonomous coating systems.
Efficient removal of CO₂ and H₂S from natural gas is essential to meet product specifications, prevent corrosion, and ensure reliable operation in gas processing facilities. However, simultaneously achieving product quality targets while minimizing total process energy (TPE), amine loss (AL), and hydrocarbon loss (HCL) under multiple operational variables remains insufficiently addressed. In this work, a validated process-based computational framework is developed for the modeling, screening, and optimization of a tri-solvent gas sweetening system comprising methyldiethanolamine (MDEA), piperazine (PZ), and sulfolane. A detailed steady-state simulation model was first established and validated against industrial data, yielding a mean absolute error of approximately 6%, confirming its suitability for predictive and optimization studies. For the first time, a large-factor statistical screening approach was applied to simultaneously evaluate 13 operational variables in a tri-solvent gas sweetening process, enabling an efficient reduction of the complex operational space. Thirteen operational variables were evaluated against performance indicators: CO₂ and H2S concentrations in the treated gas, AL, HCL, and TPE. A Plackett–Burman design (PBD) was used to identify the most influential variables, reducing the number from 13 to 9. These key factors were further analyzed and optimized using a central composite design (CCD) and analysis of variance (ANOVA), yielding predictive correlations with R² values above 0.97. The optimized operating conditions achieved a reduction of approximately 14% in specific reboiler duty while decreasing the CO₂ mole fraction in the treated gas from 0.02 to 0.00001. Simultaneously, H2S, amine, and hydrocarbon losses were maintained at low levels of approximately 9ppm, 0.9 kg·h⁻¹, and 128.36 kg·h⁻¹, respectively. These findings demonstrate that the proposed framework, combined with an effective solvent system, can simultaneously enhance product quality, reduce energy demand, and improve process stability. Overall, the presented methodology provides a validated and scalable approach for advanced optimization of gas sweetening processes, offering practical guidance for process design, operational control, and solvent selection in natural gas treatment systems.
The valorization of industrial waste into functional catalyst materials is a promising route for supporting renewable fuel production. However, the use of geothermal-sludge-derived silica as a catalyst support for hydrocracking non-edible oils remains insufficiently explored. In this study, silica-rich geothermal sludge was converted into sulfated silica (SO₄–SiO₂) and used as a support for Ni–Cu catalysts in the hydrocracking of castor oil. The catalyst was prepared through sulfation followed by sequential metal impregnation and characterized using XRD, conventional and pyridine-adsorbed FTIR, SEM–EDX, and N₂ adsorption–desorption analysis. Pyridine-FTIR identified predominantly Lewis acidity, with an accessible Lewis acid-site concentration of 0.0744 mmol g⁻¹, whereas the Brønsted-acid contribution was below the quantification limit under the applied measurement conditions.The NiCu/SO₄–SiO₂ catalyst retained a high specific surface area of approximately 199 m² g⁻¹, while SEM–EDX analysis suggested relatively distributed Ni and Cu species on the sulfated silica support. Hydrocracking experiments were performed in a batch reactor at 225–375°C under 20 bar H₂ for reaction times of up to 120 min. Under the investigated conditions, the highest conversion was 72.71 %, with liquid products distributed mainly in the gasoline-, kerosene-, and diesel-range fractions (C₅–C₂₂); diesel-range selectivity reached approximately 49.10 %. The conversion data were reasonably described by a lumped pseudo-first-order model, with apparent rate constants of 0.011–0.012 min⁻¹ and R² values above 0.92. These kinetic parameters should be interpreted as apparent descriptors rather than intrinsic rate constants. Because product selectivity was estimated from normalized GC–MS peak areas without full response-factor correction, the reported product distribution is semi-quantitative. The proposed deoxygenation and hydrocracking pathways are therefore discussed as plausible interpretations rather than confirmed mechanisms. This exploratory study indicates the potential of geothermal-sludge-derived silica as a catalyst-support precursor, while replicated catalytic testing is required to confirm performance reproducibility.
In this study, Pure and Ag/Co co-doped ZnO nanoparticles (2% and 4%) were synthesized via a green route using Citrus maxima peel extract as a natural reducing and stabilizing agent. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), UV–visible spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. XRD analysis confirmed the formation of the ZnO phase and supported possible dopant incorporation without detectable secondary crystalline phases. The crystallite size increased from 16 to 21 nm with increasing dopant concentration, while SEM analysis revealed nearly spherical nanoparticles with average particle sizes ranging from 30 to 35 nm. UV–Vis analysis showed a gradual decrease in band gap energy from 3.483 eV for pure ZnO to 3.402 eV and 3.371 eV for 2% and 4% Ag/Co co-doped ZnO, respectively. Antibacterial activity was evaluated against Escherichia coli and Staphylococcus aureus, where the 4% Ag/Co co-doped ZnO sample exhibited the highest inhibition zones at 400 µg/mL. Cytotoxicity assessment using the Brine Shrimp Lethality Assay (BSLA) indicated lower toxicity for the co-doped samples at lower concentrations compared with pure ZnO. These results demonstrate that Ag/Co co-doping significantly influences the structural, optical, antibacterial, and cytotoxic properties of ZnO nanoparticles. However, further mechanistic studies and comprehensive toxicity evaluations are required before practical applications can be established.
Thermally treated organic carbon materials offer great potential for optoelectronic and fluorescence-based sensor applications. However, optimizing emission properties through metal doping remains a challenge due to the nonlinear relationship between doping concentration and optical power. This relationship involves complex interactions between intrinsic emission, defect states, and metal-induced states. Furthermore, the spectral overlap of the excitation and emission spectra contributes to energy losses through reabsorption mechanisms, thus reducing system efficiency. In this study, the influence of copper doping on thermally treated citric acid carbon materials was investigated using a Bayesian optimization approach. The parameters analyzed include emission area, overlap integral, and emission efficiency. Spectral deconvolution was used to determine the relative contributions of intrinsic, defect, and metal emission to the total emission. Finally, hybrid surrogate modeling was applied to optimize the doping conditions, taking into account the corresponding parameter trade-offs. The results show that maximum efficiency is not achieved at the highest emission conditions, but rather at intermediate doping concentrations, where the contribution from defect states is dominant and spectral overlap is minimal. Pareto analysis reveals a clear trade-off between increasing emission intensity and minimizing energy loss. Bayesian optimization efficiently identified the optimal conditions with a limited number of experiments and recommended an optimal doping range in the intermediate region. This study demonstrates that a data-driven approach is not only effective in determining the optimal conditions but also provides mechanistic insights into the role of each emission contribution in system performance. This approach has the potential for broad application in the design of carbon-based optical materials.
Waste cooking oil (WCO) is a potential feedstock for producing renewable hydrocarbon fuels through catalytic pyrolysis. In this work, a Ni-based bimetallic catalyst supported on marble waste (MW) was prepared to convert WCO into hydrocarbon fuel without detectable carboxylic acids. The performance of NiZnMW was compared with those of NiCoMW, NiFeMW, and NiCuMW to evaluate the effect of the second metal on the catalytic activity. The catalysts were characterized using XRD, N₂ adsorption-desorption, SEM-EDX, FESEM, HR-TEM, FTIR, H₂-TPR, CO₂-TPD, XPS, and TGA. Pyrolysis was carried out at 380 °C under a nitrogen atmosphere. Among the catalysts, NiZnMW showed the best performance, with 96.6% WCO conversion, 68.93% hydrocarbon yield, and 92.28% hydrocarbon selectivity. No carboxylic acids were detected in the liquid product. The good performance of NiZnMW is related to the combined effect of Ni and Zn, the presence of basic sites and suitable pore properties, which improve the removal of oxygen-containing compounds during pyrolysis. The catalyst also remained active after four reaction cycles, with hydrocarbon selectivity remaining above 86% after four consecutive cycles. The NiZnMW catalyst prepared from marble waste showed high activity and good stability, making it a practical catalyst for producing hydrocarbon fuel from waste cooking oil.
This study investigates the upcycling of low-density polyethylene (LDPE) plastic bags and multilayer plastic (MLP) wastes into sand-plastic paving blocks and evaluates the influence of plastic type and plastic-sand ratio on their physicochemical and mechanical properties Fourier Transform Infrared Spectroscopy (FTIR) and Thermogravimetric Analysis (DSC/TG/DTG) showed that LDPE behaves as a single-polymer system with higher crystallinity, distinct melting behaviour, and greater thermal stability, whereas MLP exhibits multiple polymer phases and inorganic residues that reduce melt compatibility. Paving blocks were produced at plastic-sand ratios ranging from 100:0 to 40:60 and characterized for density, porosity, water absorption, and compressive strength. LDPE composites achieved the best performance at a 60:40 ratio, reaching a compressive strength of 25.7 MPa with water absorption below 0.4%. MLP-based blocks showed higher porosity and lower compressive strength, with a maximum value of 18.4 MPa, attributed to immiscible polymer layers and metallic impurities. Nevertheless, all samples exhibited excellent water resistance, with water absorption below 1%, outperforming conventional cement-based paving materials. These findings demonstrate that both mono-material and complex plastic wastes can be effectively upcycled into durable paving products, providing a sustainable waste valorization route that links physicochemical characteristics to engineering performance for the minimization and utilization of difficult-to-recycle plastic waste.
The removal of synthetic dyes from wastewater remains a major environmental challenge owing to their toxicity and persistence. This work investigates the adsorption of two anionic azo dyes Reactive Black 5 (RB5) and Reactive Red 141 (RR141) onto a carbon-silica hybrid (CAM) obtained as a purified residue from biogenic silica production, aiming to elucidate the underlying mechanisms and assess its potential as an efficient, low-cost adsorbent for dye-contaminated water treatment. Batch adsorption experiments were conducted to examine kinetic, equilibrium, and thermodynamic behaviors. Density Functional Theory (DFT) simulations, combined with non-covalent interaction (NCI) and quantum theory of atoms in molecules (QTAIM) analyses, were performed to explore the nature and strength of dye-surface interactions. The CAM surface was modeled with silanol (-Si-OH) and siloxane (-Si-O-Si-) groups to reflect its reactive sites. The optimal pH for adsorption was 3 for both dyes, with removal percentages exceeding 92% within 240 min. The Sips model gave the best statistical fit to the equilibrium data of both dyes; the fitted Sips heterogeneity exponent revealed a markedly heterogeneous surface for RB5 (exponent well below unity, consistent with a strong Freundlich fit) and near-monolayer behavior for RR141 (exponent close to unity at the lower temperatures). CAM exhibited maximum experimental adsorption capacities of 124.8 mg g−1 for RB5 and 109.9 mg g−1 for RR141, in the range reported for hybrid silica-carbon and activated-carbon adsorbents under comparable conditions. Negative ΔG0 and ΔH0 values confirmed spontaneous and exothermic adsorption, while the positive ΔS° values, attributed to the release of ordered hydration water and counter-ions upon dye binding, indicate that the process is also entropically favorable; the DFT analyses revealed hydrogen bonding, electrostatic attraction, and π-π stacking as the primary stabilizing forces. The synergistic integration of experimental and theoretical insights provides a robust molecular-level understanding of dye-adsorbent interactions, indicating CAM as a promising low-cost adsorbent for anionic-dye removal, whose performance under realistic wastewater conditions warrants further evaluation.
