Search Results (2,916)

Valorizing coconut shell waste as a renewable lignocellulosic precursor offers a sustainable route to produce high-performance activated carbons for wastewater treatment. In this study, coconut shells were transformed into activated carbons through physical activation (air, CO₂, steam) and chemical activation (H₃PO₄, ZnCl₂, KOH), allowing direct comparison of how each method influences porosity and surface chemistry. Among the physically activated samples, steam activation produced the best material, A-ST, with S_BET = 738 m² g⁻¹, V_mi = 0.38 cm³ g⁻¹ and V_me = 0.07 cm³ g⁻¹. KOH activation yielded the top-performing carbon, A-KOH, achieving S_BET = 1600 m² g⁻¹, V_mi = 0.74 cm³ g⁻¹, and V_me = 0.22 cm³ g⁻¹. Adsorption tests with methylene blue, methyl orange, and orange G showed a clear link between physicochemical features and dye uptake. A-ST and A-KOH exhibited the highest capacities due to their wide micro–mesoporosity and favorable surface charge at the adsorption pH. In both cases, methylene blue was most strongly retained, confirming that large aromatic cations benefit from π–π interactions with graphene-like layers and easy micropore access. Overall, the results demonstrate that coconut-shell valorization is maximized when activation enhances both porosity and surface chemistry, enabling the production of tailored sorbents for the efficient removal of organic contaminants. Full article

The Electro-Fenton (EF) process is a promising technology for the sustainable remediation of organic contaminants in complex wastewater. In this study, a weak magnetic field (~150 G) was applied to enhance the performance of an EF system using magnetite (Fe₃O₄) synthesized by a controlled co-precipitation route as a recyclable solid iron source. The magnetite was characterized by FTIR, SEM/EDS, and XPS, confirming the coexistence of Fe²⁺/Fe³⁺ species essential for in situ Fenton-like reactions. Under the selected operating conditions (90 min reaction time), magnetic-field assistance improved methylene blue decolorization from 14.2% to 46.0% at pH 3. FeSO₄ was used only as a homogeneous benchmark, whereas the magnetite-based system operated without soluble iron addition, minimizing sludge formation and secondary contamination. These results demonstrate the potential of magnetite-assisted and magnetically enhanced EF systems as a low-cost, sustainable alternative for the treatment of dye-containing industrial wastewater and other complex effluents. Full article

This work presents a green chemistry route to obtain titanium dioxide TiO₂ nanoparticles with an average size of about 13.25 nm using lemongrass (Cymbopogon citratus) extract. For these assessments, TiO₂ nanoparticles were added to the coating at concentrations of 1% and 5% w/w on fiber-cement sheets. Self-cleaning evaluation was analyzed by the photodegradation of methylene blue (MB) dye at concentrations of 5, 10, and 20 mg/L applied to the coated sheet, and then exposed to simulated sunlight. The coating containing 5 wt% TiO₂ nanoparticles showed the highest photodegradation, reaching 93.3% after 4 h under simulated sunlight exposure at the lowest MB concentration (5 mg/L). Additionally, average contact angles of 80.4°, 92.03°, and 104.25° were determined for coatings containing 0%, 1%, and 5 wt% TiO₂, respectively. Moreover, the modified 5 wt% TiO₂ exhibited up to 30.9% greater hydrophobicity than the control. Antifungal efficacy against Aspergillus niger and Penicillium was evaluated using the Poisoned Food method with nanoparticles at concentrations of 1 and 3 mg/mL showing a moderate growth inhibition. In conclusion, the versatility demonstrated suggests potential applications such as a nano-additive for aqueous acrylic coatings, improving hydrophobicity, self-cleaning and antifungal properties, which could be attractive to the construction industry. Full article

Titanium oxide (TiO₂) is of great interest in solar cell manufacturing, hydrogen production, and organic compound photodegradation. The synthesis variables and methodology affect the morphology, texture, crystalline structure, and phase mixtures of TiO₂, which, in turn, affect the optical and catalytic properties of TiO₂. In this work, the effect of acetic acid as a catalyst and chelating agent on the morphology, texture, crystal structure, optical properties, and photocatalytic activity of TiO₂ samples obtained using the sol–gel method with sodium dodecyl sulfate (SDS) as a template was investigated. The results indicated that acetic acid not only catalyzes the hydrolysis of the TiO₂ precursor but also acts as a chelating agent, causing a decrease in crystallite size from 18.643 nm (T7 sample, pH = 6.8, without addition of acetic acid) to 16.536 nm (T2 sample, pH = 2). At pH 2 and 3, only the anatase phase was formed (T2 and T3 samples), whereas at pH 5 and 6.8, in addition to the anatase phase, the brookite phase (11.4% and 15.61% for samples T5 and T7, respectively) was formed. The band-gap value of TiO₂ decreased with decreasing pH during synthesis. Although the T2 sample had the highest specific surface area and pore volume (232.02 m²g⁻¹ and 0.46 gcm⁻³, respectively), the T3 sample had better efficiency in methylene blue dye photodegradation because its bird-nest-like morphology improved photon absorption, promoting better photocatalytic performance. Full article

The increasing discharge of recalcitrant organic dyes from the textile industry necessitates the development of efficient and sustainable wastewater treatment technologies. This study reports the successful eco-friendly fabrication of magnetically separable cerium–manganese ferrite (Ce-MnFe₂O₄) nanocatalysts via a one-pot green synthesis route, utilizing an aqueous extract of Brachychiton populneus leaves. The structural, morphological, magnetic, and optical properties of the synthesized nanocatalysts were systematically investigated. X-ray diffraction (XRD) analysis confirmed the formation of a phase-pure cubic spinel structure, with evidence of Ce³⁺ ion incorporation leading to lattice expansion and the formation of beneficial oxygen vacancies. The composite material exhibited superparamagnetic behavior with a high saturation magnetization of 38.7 emu/g, which facilitates efficient magnetic separation and recovery. Optical studies revealed a direct bandgap of 2.33 eV, enabling significant photocatalytic activity under visible light irradiation. The Ce-MnFe₂O₄ nanocatalyst demonstrated superior performance, achieving degradation efficiencies of 96% for methylene blue and 98% for Congo Red within 90 min. Furthermore, the catalyst demonstrated good operational stability, maintaining 62% of its initial degradation efficiency for CR and 51% for MB after five consecutive reuse cycles. These results underscore the potential of this green-synthesized, magnetically recoverable nanocatalyst as a highly effective and sustainable solution for the remediation of dye-contaminated industrial effluents. Full article

Although carbon filters (CF) can exhibit limited adsorption/selectivity for certain emerging pollutants and operating conditions, incorporating carbon–metal-oxide composites provides a platform to study how surface chemistry, charge distribution and oxide dispersion influence adsorption behavior. This study investigates the incorporation of metal oxides (Fe₃O₄, TiO₂ and CaO) into a commercial carbon filter via mechanical milling, focusing on fundamental changes in surface properties and methylene blue (MB) adsorption mechanisms. The synthesized oxides were characterized by X-ray diffraction and scanning electron microscopy, confirming crystalline structures with crystalline sizes between 11 and 23 nm. Composite filters with varying oxide contents (10–30 wt%) were evaluated for point of zero charge (PZC), surface charge distribution and methylene blue (MB) adsorption. The kinetic experiments were adjusted to pseudo-second order (PSO). Although the maximum adsorption capacity (2.75 mg·g⁻¹ for CaO-modified filters) is lower than commercially activated carbons, this work clarifies how oxide type and dispersion control adsorption performance and interaction mechanisms. Langmuir and Freundlich models revealed monolayer adsorption with favorable dye-surface interactions. These models provide key insights into the role of oxide type and pH in the dye removal process. Full article

A composite based on θ-Al₂O₃ microspheres coated with graphene oxide (GO) and reduced graphene oxide (RGO) was prepared and evaluated as a sorbent for the removal of synthetic dyes from aqueous solutions. GO was synthesized by a modified Hummers’ method and deposited onto alumina microspheres via ultrasound-assisted treatment under various conditions, followed by supercritical reduction to obtain the Al₂O₃_RGO composite. The structure, morphology, and composition of the materials were characterized by Raman spectroscopy, SEM, TGA/DSC, FTIR, and XRD, revealing the formation of mono- and few-layer GO/RGO coatings on the substrate surface. Adsorption tests for cationic methylene blue (MB) dye and anionic methyl orange (MO) dye demonstrated that the alumina substrate was inactive, whereas GO- and RGO-coated microspheres exhibited high adsorption efficiency for MB and partial uptake of MO from water solutions. In mixed-dye solutions, both Al₂O₃_GO and Al₂O₃_RGO composites showed selectivity toward MB, and the RGO-based composite demonstrated enhanced MB adsorption at low concentrations. The results highlight GO/RGO-coated θ-Al₂O₃ microspheres as convenient and selective composite sorbents for water purification processes. Full article

Spent coffee grounds (SCGs) are abundantly produced worldwide as a by-product of coffee brewing, and production is surging following the rise in global coffee consumption. Although the adsorption properties of raw SCGs have been investigated in previous studies, limited attention has been paid to the use of SCG-derived hydrochars as engineered adsorbents. In this work, hydrochars produced via hydrothermal carbonization (HTC) of SCGs at different temperatures were systematically assessed for their capacity to remove methylene blue (MB) dye from aqueous solution. The effect of HTC temperature and soft alkaline activation on MB adsorption were evaluated through adsorption batch tests. The soft alkaline activation increased the experimental adsorption capacity from <20 mg g⁻¹ for untreated hydrochars to approximately 100 mg g⁻¹ at 20 °C, while Langmuir isotherm analysis yielded a monolayer capacity of 147.1 mg g⁻¹ at the same temperature; experimental uptake further increased to 215.6 mg g⁻¹ at 40 °C and high dye concentrations. Kinetic, isotherm, and thermodynamic tests were performed on selected materials to describe their adsorption behavior and potential mechanisms. Microscopic, diffraction, spectroscopic, and porosimetric analyses were performed to investigate the structural differences among the tested materials. This study shows that temperature regulation and soft alkaline activation can strongly improve the adsorption capacity of the hydrochars, producing competitive low-cost adsorbents from a waste material in compliance with the principles of the circular economy. Full article

TS-1 zeolite and a series of Zr-modified samples (TS-1/xZr) were synthesized and systematically characterized to investigate the influence of zirconium incorporation on structural, textural, and photocatalytic properties. The structural and textural properties of the samples were examined by XRD and nitrogen adsorption isotherms. Elemental analysis (EDXRF, SEM/EDS) and FTIR confirmed successful incorporation of Zr into the TS-1 framework. Photocatalytic tests under white light irradiation using crystal violet (CV), methylene blue (MB), rhodamine B (RhB) and methyl orange (MO) dyes revealed enhanced degradation efficiency for the Zr-containing samples, particularly TS-1/10Zr. Kinetic modeling using pseudo-first-order (PFO) and pseudo-second-order (PSO) approaches indicated that dye degradation followed mainly PSO kinetics. Reusability studies demonstrated sustained stability and recyclability of the catalysts. The improved photocatalytic performance is attributed to synergistic electronic effects between Ti and Zr species, which enhance charge separation and light absorption. Full article

Mesoporous carbons based on silica hard templates were used to investigate physical processes in confined pores. Nitrogen adsorption, scanning electron microscopy, and scattered X-ray analyses revealed two classes of materials: carbons with moderate and highly developed mesoporosity. The pore structure was strongly dependent on pore expanders which proved essential for generating open, accessible architectures. All carbons exhibited a basic, graphitic surface (pH_PZC = 8.4–10.9), enriched in electron-donating oxygen functionalities. Differential scanning calorimetry studies of confined water showed that melting point depression follows the Gibbs–Thomson relationship, confirming the strong dependence of phase transitions on pore size and water–surface interactions. Adsorption experiments using methylene blue demonstrated that capacity is governed by surface area, pore volume, and pore size distribution. For carbon with the largest average pore size, adsorption of various dyes revealed that uptake decreases with increasing molecular size, whereas affinity depends strongly on electrostatic interactions. Kinetic studies indicated that carbons with larger mesopores exhibit the fastest adsorption, and that large, complex dye molecules undergo significant diffusion limitations. Overall, the results show that the interplay between pore structure, adsorbate size, and surface chemistry influences both the equilibrium uptake and adsorption kinetics in mesoporous carbon materials. Full article

This study presents a green synthesis of zinc oxide (ZnO) nanoparticles (NPs) capped with Haloxylon (P1) and Calligonum (P2) extracts. The use of plant-derived biomolecules as natural capping agents offers an environmentally friendly strategy to tune surface chemistry and to enhance the photocatalytic behavior of ZnO NPs. ZnO/plant extracts nanocomposites were prepared via a hydrothermal route and systematically characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), UV–Vis spectroscopy, and photoluminescence (PL), followed by evaluation of their photocatalytic performance against methylene blue (MB) under UV irradiation. XRD confirmed a wurtzite structure with crystallite sizes ranging from 8.95 to 10.93 nm, while PL spectra indicated an improved charge carrier separation in extract-capped ZnO. The characteristics and pollutant removal performance of the greenly synthesized ZnO composites were compared with those of a chemically synthesized ZnO nanoparticles reference sample. Adsorption tests under dark conditions revealed a strong difference between the materials: ZnO-P1 removed 48% of MB, whereas ZnO-P2 adsorbed only 7%, demonstrating a much higher affinity of the Haloxylon-derived surface groups toward MB. In comparison, the chemically synthesized ZnO exhibited an adsorption capacity of 54%, confirming that the Haloxylon-mediated surface provides a comparable efficient dye uptake prior to irradiation. After UV irradiation, all samples exhibited a photocatalytic activity with a total MB removal reached ~59% for the reference ZnO sample and ~53% for ZnO-P1 compared to about 13% for the ZnO-P2. Kinetic analysis also confirmed that ZnO-P1 possessed a high degradation rate constant, indicating a better intrinsic photocatalytic efficiency in addition to the strong adsorption contribution. The enhanced performance of plant-capped ZnO is attributed to phytochemical-induced surface defects, which facilitated charge separation and boosted the generation of reactive oxygen species (ROS). Overall, these results demonstrate that Haloxylon and Calligonum extracts are effective and sustainable capping agents, providing a low-cost, eco-friendly approach for designing ZnO nanocatalysts composites with promising applications in wastewater treatment and environmental remediation. Full article

A geopolymer, derived from agricultural waste, was used as an efficient, sustainable, and low-cost adsorbent of methylene blue, a recurrent industrial dye contaminant. The geopolymer was synthesized via a standard alkali activation process using wheat husk ash calcinated at 1050 °C. Adsorption capabilities were evaluated through batch kinetic experiments. The removal efficiency was determined by ultraviolet–visible spectrophotometry, and the adsorption kinetics were fitted to various models. The geopolymer demonstrated a maximum adsorption capacity of 270.58 mg/g for methylene blue, achieving a removal efficiency of 85.20% under optimal conditions. Kinetic analysis confirmed that the adsorption process is best described by the pseudo-second-order model. This suggests that chemisorption, which involves chemical bonding or electron exchange between the dye and the negatively charged aluminosilicate structure of the geopolymer, is the rate-limiting mechanism. This demonstrates that geopolymers are effective and promising adsorbents, valorizing an agricultural waste stream into a functional material for the efficient treatment of dye-polluted wastewater. The competitive capacity and favorable chemisorption mechanism position the geopolymer as a promising material for the remediation of dye-contaminated industrial effluents. Full article

ZnO semiconductor-based photocatalysts are mainly studied for the elimination of toxic textile dyes. Metal-doped ZnO displays better performance for this purpose. Herein, Al-doped ZnO (Al–ZnO) was prepared using the mechanochemical calcination method with varying aluminum concentrations for the degradation of the persistent methylene blue (MB) dye. Various characterization techniques, including XRD, FTIR, FESEM, TEM, UV-DRS, and XPS, revealed the improved properties of 3% Al–ZnO in degrading the MB dye. It exhibits 96.56% degradation of 25 mg/L MB dye under 60 min of natural sunlight irradiation with a catalyst dose of 0.5 g/L at a natural pH of 6.4. A smaller particle size, a lower band gap energy of 3.264 eV, and the presence of oxygen vacancies and defect states all facilitate photocatalytic degradation. Radical scavenger experiments using ascorbic acid (for •O₂⁻), 2-propanol (for •OH), and diammonium oxalate (for h⁺) confirmed the crucial role of superoxide (•O₂⁻) and hydroxyl (•OH) radicals in the degradation mechanism. The achievement of 82.80% MB degradation efficiency at the 4th cycle validates the notable stability and excellent reusability of Al–ZnO. Full article

The use of activated carbon (AC) in environmental applications, particularly for water and air purification, is highly valued due to its excellent microstructural and adsorption properties. However, its powdered form presents significant challenges in industrial applications, such as difficulty in handling and potential environmental risks due to its tendency to disperse easily. To overcome these issues, converting activated carbon into a more industrially viable form, such as pellets, is crucial. In this study, pelletizing AC within a crosslinked polyvinyl alcohol–diglycidyl ether of bisphenol A (PVA–DGEBA) matrix enabled the production of structurally stable cylindrical pellets through the formation of a robust three-dimensional polymeric network. This approach required minimal binder usage and facilitated processing at relatively low temperatures, effectively overcoming common disintegration issues associated with traditional pelletization methods reliant on linear polymer binders and compression-based techniques. The resulting pellets exhibited methylene blue (MB) adsorption (q max ~14.8 mg/g of pellet), which is about 50% of the initial AC’s adsorption capability, and retained structural integrity across multiple aqueous cycles. They also remained stable in methanol, ethanol and acetone by showing no observable disintegration, which highlights their excellent stability. Comprehensive characterizations, including hardness tests, swelling behavior, and various structural evaluations, revealed a mechanical strength of 3.37 ± 0.46 MPa and an adsorption volume of ~250 cm³/g through Brunauer–Emmett–Teller analysis, confirming effective crosslinking and the adsorption capabilities of the pellets. This eco-friendly and stable pelletization strategy demonstrated great potential for low-temperature pelletizing of AC, ensuring advanced applications in wastewater treatment even under pressurized conditions, presenting a significant improvement over the traditional method. Full article

A cobalt-containing zeolitic imidazolate framework (ZIF-67) was carbonized by different routes to composite materials (cZIFs) composed of metallic Co, Co₃O₄, and N-doped carbonaceous phase. The effect of the carbonization procedure on the water pollutant removal properties of cZIFs was studied. Higher temperature and prolonged thermal treatment resulted in more uniform particle size distribution (as determined by nanoparticle tracking analysis, NTA) and surface charge lowering (as determined by zeta potential measurements). Surface-governed environmental applications of prepared cZIFs were tested using physical (adsorption) and electrochemical methods for dye degradation. Targeted dyes were methylene blue (MB) and methyl orange (MO), chosen as model compounds to establish the specificity of selected remediation procedures. Electrodegradation was initiated via an intermediate reactive oxygen species formed during oxygen reduction reaction (ORR) on cZIFs serving as electrocatalysts. The adsorption test showed relatively uniform adsorption sites at the surface of cZIFs, reaching a removal of over 70 mg/g for both dyes while governed by pseudo-first-order kinetics favored by higher mesoporosity. In the electro-assisted degradation process, cZIF samples demonstrated impressive efficiency, achieving almost complete degradation of MB and MO within 4.5 h. Detailed analysis of energy consumption in the degradation process enabled the calculation of the current conversion efficiency index and the amount of charge associated with O₂^•−/^•OH generation, normalized by the quantity of removed dye, for tested materials. Here, the proposed method will assist similar research studies on the removal of organic water pollutants to discriminate among electrode materials and procedures based on energy efficiency. Full article