Search Results (409)

Dye residues from the textile industry constitute a critical wastewater problem. This study aimed to evaluate the removal capacity of methylene blue (MB) in aqueous media, using an adsorbent formulated from activated and sonicated nanoclay (NC) and microatomized Nostoc sphaericum (ANS). NC was obtained by acid treatment, followed by activation with 1 M NaCl and sonication, while ANS was obtained by microatomization in an aqueous medium. NC/ANS was mixed in a 4:1 weight ratio. The NC/ANS synergistic adsorbent was characterized by the point of zero charge (PZC), zeta potential (ζ), particle size, FTIR spectroscopy, and scanning electron microscopy (SEM). NC/ANS exhibited good colloidal stability, as determined by pH_PZC, particle size in the nanometer range, and heterogeneous morphology with functional groups (hydroxyl, carboxyl, and amide), removing between 72.59 and 97.98% from an initial concentration of 10 ppm of MB, for doses of 20 to 30 mg/L of NC/ANS and pH of 5 to 8. Optimal adsorption conditions are achieved at pH 6.8 and 32.9 mg/L of adsorbent NC/ANS. It was observed that the pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models best described the adsorption kinetics, indicating a predominance of the physisorption process, with adsorption capacity around 20 mg/g. Isotherm models and thermodynamic parameters of adsorption, ΔS, ΔH, and ΔG, revealed that the adsorption process is spontaneous, favorable, thermodynamically stable, and occurs at the monolayer level, with a regeneration capacity of 90.35 to 37.54% at the fifth cycle. The application of physical activation methods, such as sonication of the clay and microatomization of the algae, allows proposing a novel and alternative synergistic material from organic and inorganic sources that is environmentally friendly and promotes sustainability, with a high capacity to remove cationic dyes in wastewater. Full article

In this work, biochars were produced by pyrolysis of exhausted olive pomace and evaluated as low-cost adsorbents for the removal of methylene blue (MB) from aqueous solutions. The biochar obtained at 400 °C for 1 h, which exhibited the best adsorption performance, was characterized by FTIR, N₂ adsorption–desorption isotherms, SEM-EDX, and proximate analysis, revealing a mesoporous structure with a relatively low specific surface area but enriched in surface functional groups, likely due to the partial degradation of lignocellulosic components. Adsorption experiments were conducted to optimize operational parameters such as solid particle size (2–3 mm), agitation speed (75 rpm), and bioadsorbent dosage (1 g per 0.05 L of MB solution), which allowed for dye removal efficiencies close to 100%. Kinetic studies showed that MB adsorption followed a pseudo-second-order model, while equilibrium data at 30 °C were best described by the Langmuir isotherm (R² = 0.999; SE = 4.25%), suggesting monolayer coverage and strong adsorbate–adsorbent affinity. Desorption trials using water, ethanol, and their mixtures resulted in low MB recovery, whereas the addition of 10% acetic acid significantly improved desorption performance. Under optimal conditions, up to 52% of the retained dye was recovered. Full article

This study presents research on the production of activated biocarbons derived from herbal waste. Sage stems were chemically activated with two activating agents of different chemical natures—H₃PO₄ and K₂CO₃—and subjected to two thermal treatment methods: conventional and microwave heating. The effect of the activating agent type and heating method on the basic physicochemical properties of the resulting activated biocarbons was investigated. These properties included surface morphology, elemental composition, ash content, pH of aqueous extracts, the content and nature of surface functional groups, points of zero charge, and isoelectric points, as well as the type of porous structure formed. In addition, the potential of the prepared carbonaceous materials as adsorbents of model organic (represented by Triton X-100 and methylene blue) and inorganic (represented by iodine) pollutants was assessed. The influence of the initial adsorbate concentration (5–150 (dye) and 10–800 mg/dm³ (surfactant)), temperature (20–40 °C), and pH (2–10) of the system on the efficiency of contaminant removal from aqueous solutions was evaluated. The adsorption kinetics were also investigated to better understand the rate and mechanism of contaminant uptake by the prepared activated biocarbons. The results showed that materials activated with orthophosphoric acid exhibited a significantly higher sorption capacity for all tested adsorbates compared to their potassium carbonate-activated counterparts. Microwave heating was found to be more effective in promoting the formation of a well-developed specific surface area (471–1151 m²/g) and porous structure (mean pore size 2.17–3.84 nm), which directly enhanced the sorption capacity of both organic and inorganic contaminants. The maximum adsorption capacities for iodine, methylene blue, and Triton X-100 reached the levels of 927.0, 298.4, and 644.3 mg/g, respectively, on the surface of the H₃PO₄-activated sample obtained by microwave heating. It was confirmed that the heating method used during the activation step plays a key role in determining the physicochemical properties and sorption efficiency of activated biocarbons. Full article

Dye-sensitized solar cells (DSSCs) have emerged as a promising technology for converting sunlight into electricity at a low cost; however, it is still necessary to find a photostable, low-cost, and efficient photosensitizer. In this sense, the natural product bixin (Dye 1) has previously been reported as a potential photosensitizer. Thus, the present work reports the full synthesis of diester and diacid hybrids (Dyes 2 and 3, respectively, with corresponding yields of 93% and 52%) using the natural product bixin as a starting material and 1,3,4-oxadiazole ring as a connected point. The hydrolysis step of Dye 2 aims to obtain Dye 3 with a structural capacity to anchor the titanium dioxide (TiO₂) nanofilms via the carboxylic acid group. Both compounds (Dyes 1 and 3) can be adsorbed via pseudo-first order on the surface of TiO₂ nanofilms, reaching saturation after 10 and 6 min of exposure in an organic solution (1 × 10⁻⁵ M), respectively, with adsorption kinetics of the semisynthetic compound almost twofold higher than the natural product. Contrary to expectations, Dye 3 had spectral behavior similar to Dye 1, but with better frontier molecular orbital (FMO) parameters, indicating that Dye 3 will probably behave very similarly or have slightly better photovoltaic performance than Dye 1 in future DSSC measurements. Full article

The treatment with an alkali (sodium hydroxide) solution of acid-activated montmorillonite clay minerals resulted in a reduction in specific surface area. However, a significant enhancement in the removal of basic blue-41 dye solution was achieved compared to acid-activated samples only (first step of activation) and to the raw montmorillonite clay. The obtained products were characterized using different techniques. The results indicated that the acid-activated montmorillonites exhibited different physicochemical properties than the starting raw montmorillonite, with a reduction in the cation exchange capacity and improvements in the specific surface area (from 5 m²/g to 274 m²/g) and total pore volume (from 0.031 cm³/g to 0.450 cm³/g) due to the formation of the amorphous silica phase. However, the treatment with NaOH solution was accompanied by significant reductions in the specific surface area (from 274 m²/g to 18 m²/g) and total pore volume (from 0.450 cm³/g to 0.02 cm³/g) due to the dissolution of the formed amorphous silica phase, as confirmed through ²⁹Si MAS NMR and FTIR techniques. In addition, the SiO₂/Al₂O₃ molar ratios were close to those of the starting montmorillonite clay. The removal of the cationic basic blue-41 was optimized under different conditions, such as different initial concentrations, adsorbent doses, and pHs of the dye solution. The maximum removal capacities of acid-activated clays were in the range of 45 mg/g to 80 mg/g and decreased with the extent of the acid activation process. However, the capacities were enhanced after NaOH treatment and reached values in the range of 80 to 120 mg/g. Enhancing the surface area had less of an impact on the materials’ removal ability. The obtained materials performed well in seven adsorption–regeneration cycles, showing a 70% reduction in removal effectiveness. Full article

Nowadays, there is an urgent need for efficient photocatalysts and adsorbents for environmentally relevant applications. This study investigates the effect of polyaniline (PANI) on the structure and performance of carbonized nanocomposites composed of PANI and TiO₂ nanotubes (NTs), focusing on their photocatalytic degradation efficiency and dye adsorption capacity. The hypothesis was that PANI forms conductive carbon domains and stabilizes the anatase phase during thermal treatment, enhancing the performance of TiO₂-NTs as photocatalysts. Nanocomposites based on PANI and TiO₂-NTs (TTP) were synthesized through chemical oxidative polymerization of aniline (ANI) in the presence of TiO₂-NTs using two TiO₂/ANI molar ratios of 50 and 150 and subsequently carbonized at 650 °C, yielding CTTP-50 and CTTP-150. The novel CTTP composites and carbonized pristine TiO₂-NTs (CTNT) were characterized by various techniques, including TEM, UV-Vis diffuse reflectance, Raman spectroscopy, XRD, and TGA. Their performance regarding dye adsorption and photocatalytic degradation under visible light was evaluated with Acid Orange 7, Methylene Blue, and Rhodamine B. CTTP-150 exhibited the highest adsorption capacity and photodegradation rate, attributed to the synergistic effect of PANI, which stabilizes the TiO₂ phase and enhances visible-light absorption and adsorption. Full article

A cellulose-based material with high adsorption capacity and surface area was developed by selecting appropriate copolymer monomers for structural design. This material was used for selective dye adsorption in wastewater treatment. The copolymer was characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FTIR) to investigate its microstructure, structure, thermal stability, and thermal decomposition. We explored the factors affecting dye adsorption, including dye type, adsorption reaction time, initial dye concentration, copolymer dosage, temperature, and the acidity or alkalinity of the reaction environment. The results showed that as the adsorption reaction time increased, the amount of adsorbed Rhodamine B dye gradually increased, and the initial stage (0–20 min) increased rapidly. When the initial dye concentration was 15 mg/L, the adsorption capacity (q_e) was at its maximum (3.67 mg/g). In addition, when the amount of copolymer used was 5 mg/10 mL, the adsorption capacity (q_e) was the highest (12.37 mg/g). High-temperature conditions were favorable for adsorption, with the maximum adsorption capacity (q_e) at 35 °C (13.48 mg/g). The prepared copolymer exhibited significant adsorption performance in acidic environments (pH = 3). The polymer adsorbed with dye was degraded by UV irradiation, avoiding secondary pollution caused by recycling. Full article

This study investigates the combined application of coagulation–flocculation–sedimentation (CFS) and adsorption using corncob (CC) biosorbent for the removal of textile dyes from aqueous solutions. Two synthetic dyes Bemacron Blue RS 01 (BB-RS01), a disperse dye, and Bemacid Marine N-5R (BM-N5R), an acid dye were selected for evaluation. The coagulation–flocculation process utilized aluminum sulfate as the coagulant and Superfloc 8396 as the flocculant, with operational parameters including coagulant concentrations ranging from 50 to 600 mg/L, flocculant concentrations between 30 and 125 mg/L, and pH levels spanning from 2 to 11. The corncob biosorbent was characterized using FTIR, SEM, BET, TGA/DTA, and pHpzc analyses. Adsorption isotherm experiments indicated a more favorable correlation with the Langmuir model (R² = 0.92–0.96), which supports monolayer adsorption. At pH 8, the CFS process achieved a dye removal efficiency of 95.1% for BB-RS01 and 92.3% for BM-N5R was achieved at pH 6.5. The maximum adsorption capacities of BB-RS01 were determined to be 99.5 mg/g, while BM-N5R was found to be 46.08 mg/g. These results indicate that the integration of CFS with raw corncob adsorption provides a cost-effective and efficient method for the remediation of textile dyes. Full article

The present study deals with the fabrication of activated carbon from longan peels (LPAC) using a phosphoric acid (H₃PO₄) activation method and an evaluation of LPAC’s capability for the adsorption of Reactive Black 5 (RB5) dye from aqueous solutions. The synthesized LPAC was characterized using XRD, SEM, FT-IR, and EDX, confirming a porous, carbon-rich structure with the dominant elemental composition of carbon (85.21%) and oxygen (12.43%), and a surface area of 1202.38 m²/g. Batch adsorption experiments revealed that optimal performance was achieved at pH 3.0, with equilibrium reached after 240 min. The experimental data were well fitted to the Elovich model p, suggesting a heterogeneous adsorption process with diffusion limitations. The intraparticle diffusion model further supported a multi-stage mechanism involving both film diffusion and intraparticle transport. Isotherm studies conducted at varying temperatures (293–323 K) showed a maximum adsorption capacity exceeding 370 mg/g. The adsorption data fit best with the Freundlich (R² = 0.962) and Temkin (R² = 0.970) models, indicating multilayer adsorption on a heterogeneous surface. Thermodynamic analysis revealed that the adsorption process was spontaneous and endothermic, with ΔG° values ranging from −23.15 to −26.88 kJ/mol, ΔH° = 14.23 kJ/mol, and ΔS° = 0.127 kJ/mol×K, consistent with physisorption as the dominant mechanism. Predictive modeling using an artificial neural network (ANN) achieved superior accuracy (R² = 0.989 for RRE; R² = 0.991 for q) compared to multiple linear regression (MLR). Calculation from ANN indicated that pH and contact time were the most influential factors for RB5 removal efficiency, while initial dye concentration and temperature were most critical for adsorption capacity. Furthermore, LPAC demonstrated excellent reusability, retaining over 83% removal efficiency after five adsorption–desorption cycles. These findings confirm that LPAC is an efficient and renewable adsorbent for the treatment of RB5 dye in wastewater treatment applications. Full article

Recently, graphene oxide (GO) has been largely investigated as a potential adsorbent towards dyes. However, the major obstacle to its full employment is linked to its natural powder consistence, which greatly complexifies the operations of recovery and reuse. With the aim to overcome this issue, the present work reports on the design of GO-modified carbon nanotubes buckypapers (BPs), in which the main component, GO, is entirely entrapped in the BP grid generated by CNTs for the double purpose of (a) increasing adsorption performance of GO-BPs and (b) ensure a fast process of regeneration and reuse. Adsorption experiments were performed towards several dyes: Acid Blue 29 (AB29), Crystal Violet (CV), Eosyn Y (EY), Malachite Green (MG), and Rhodamine B (RB) (C_i = 50 ppm, pH = 6). Results demonstrated that adsorption is strictly dependent on the charge occurring both on GO-BP and dye surfaces, observing great adsorption capacities towards MG (493.44 mg g⁻¹), RB (467.35 mg g⁻¹), and CV (374.53 mg g⁻¹), due to the best coupling of dye cationic form with negative GO-BP surface. Adsorption isotherms revealed that dyes capture onto GO-BPs is thermodynamically favored (ΔG < 0), becoming more negative at 313 K. Kinetic studies evidenced that the process can be described through a pseudo-first-order model, with MG, RB, and CV exhibiting the highest values of k₁. In view of these results, the following trend in GO-BP adsorption performance has been derived: MG ≈ RB > CV > AB29 > EY. Full article

Spent coffee grounds (SCG) are produced in large quantities during coffee brewing, contributing to environmental concerns. Additionally, cationic dyes from textile, paper, and leather wastewater pose a major pollution issue. This study explores SCG as an adsorbent for methylene blue (MB) dye. A novel comparison of SCG cleaning methods with warm water, accelerated solvent extraction (ASE), supercritical fluid extraction (SFE), and ultrasound-induced cavitation (US) is presented. In addition, the chemical modifications of SCG using acetylation, acid (HNO₃), and base (KOH) treatment that have not been reported before are presented. ATR-FTIR confirmed the inclusion of functional groups, for example, the nitro group in SCG treated with HNO₃, and an increase in carboxylic groups in the samples treated with KOH and HNO₃. SEM analysis revealed a consistent porous texture across samples, with SCG-SFE, SCG-US, and SCG-HNO₃ showing smaller pores, and SCG-ASE displaying elongated cavities. Adsorption isotherm tests followed the Freundlich and Langmuir models, indicating favorable adsorption. The Langmuir maximum adsorption capacity (q_max) varied among cleaning methods from 65.69 mg/g (warm water) to 93.32 mg/g (SFE). In contrast, in base- and acid-treated SCG, a three- to four-fold increase in adsorption capacity was observed, with q_max values of 171.60 mg/g and 270.64 mg/g, respectively. These findings demonstrate that SCG washed with warm water and chemically treated achieves adsorption capacities comparable to other biosorbents reported in the literature. Therefore, SCG represents a promising, low-cost, and sustainable material for removing cationic dyes from wastewater, contributing to waste valorization and environmental protection. Full article

In this research, a nanoscale magnetic biosorbent was synthesized by incorporating magnetic nanoparticles (Fe₃O₄ NPs) into a natural carbon framework derived from black cumin (BC) seeds. The prepared Fe₃O₄/BC was utilized as a low-cost, eco-friendly, and reusable nanobiosorbent for the removal of organic (e.g., methylene blue (MB) dye) pollutants from synthetic solutions. The results indicated that Fe₃O₄/BC had extensive surface oxygenous functional groups with a high affinity for MB dye capture at different concentrations such as 10–60 mg L⁻¹. The optimization results suggested the removal of ~99% of methylene blue from its initial concentration (i.e., 10 mg L⁻¹) using 2.0 g L⁻¹ of Fe₃O₄/BC at pH = 7, temperature = 27 °C, and contact time = 120 min, with equilibrium adsorption capacity = 5.0 mg g⁻¹ and partition coefficient = ~57.0 L g⁻¹. The equilibrium adsorption efficacy at the highest initial concentration (i.e., 60.0 mg L⁻¹) was found to be 29.0 mg g⁻¹. The adsorption isotherm was well explained by the Freundlich model for MB. The renderability of this magnetic bioadsorbent by acid treatments showed a ~66% decline in removal efficiency (%) (~99% to ~33%; ~5.0 to ~1.7 mg g⁻¹) for MB after six repetitive cycles of adsorption and desorption. The current Fe₃O₄/BC gives a better partition coefficient than previously reported acid-washed BC seeds and other BC-seed-based nanobioadsorbents, Hence, a synthesized Fe₃O₄/BC nanobiosorbent demonstrates potential for use in treating water contaminated with organic pollutants. Full article

Polyethylene imine (PEI) is a synthetic water-soluble and nitrogen-rich polymer with an ethylene amine repeating unit. It exists in a linear or branched forms and finds applications in various areas. PEI is often chemically modified by crosslinking reactions using molecular and polymeric crosslinkers (e.g., trichlorotriazine, epichlorohydrin, ethylene glycol diglycidyl ether, poly(ethylene glycol) diglycidyl ether, etc.) to increase its stability and reduce its water solubility. PEI (pristine/crosslinked) has a strong affinity for metal cations (e.g., Cu²⁺, Au³⁺, Pb²⁺, etc.), where the nitrogen atoms interact with the metal ions, and hence is suitable to remove metals from water with high efficiency. A thin film of crosslinked PEI on substrates can be prepared and finds diverse applications such as in removing metals and dyes, and biofouling prevention in the marine environment. The copper ion, as an example, can be stored (adsorbed) in a thin film of crosslinked PEI on a carbon cloth substrate, which can be released to water by passing an electric current through the film or with an acid treatment. It has also been reported that crosslinked PEI and composite materials can be used for the adsorption of dyes and gases such as CO₂ and SO₂ from the environment. The performance of pristine/composite/crosslinked PEI in gas, metal ion, and dye adsorption is affected by several factors. The focus of this review is to discuss the different reactions used to crosslink PEI and review the properties of the crosslinked materials and their applications. Studies have shown that the properties of the crosslinked PEI and hence its success in capturing metal ions, dyes, and CO₂ is dependent not only on the type of crosslinker but also on the degree of crosslinking. Full article

The pyrolysis carbon black (CBp) from waste tires contains zinc, iron, and other metal elements, which have high recycling value. This study proposes a simple method of recovering zinc and iron from waste tire-derived CBp to synthesize hydrotalcite-type adsorbents for the treatment of anodic dye wastewater. Firstly, zinc-aluminum hydrotalcite (LDH) and zinc-iron aluminum hydrotalcite (FeLDH) were obtained by leaching the zinc and iron ions from CBp with an acid solution. As compared with LDH, FeLDH shows increased laminate metal ion arrangement density and layer spacing. By calcining the LDH and FeLDH at 500 °C, zinc aluminum oxides (LDO) and zinc iron aluminum oxides (FeLDO) were then prepared and applied for the adsorption of dye methyl orange (MO). The results demonstrate that the maximum adsorption capacity of LDO and FeLDO are 304.9 and 609.8 mg g⁻¹ at pH of 4.0, respectively. The adsorption processes of both LDO and FeLDO are consistent with the Langmuir adsorption isotherm and the proposed second-order kinetic model. The adsorption regeneration performance and adsorption mechanism of LDO and FeLDO were also investigated in detail. Regeneration experiments show that after three cycles, the removal rate of MO by LDO remains above 80%, while that of FeLDO only remains around 64% in the first cycle after regeneration. This work would provide a new pathway to realize the high-value metal recycling of waste tire-derived CBp and solve the contamination of dye wastewater. Full article

Rapid industrialization has led to significant environmental challenges, particularly in wastewater treatment, where the removal of heavy metal ions and organic dyes is critical. This study presents the synthesis and characterization of a high-performance hydrogel adsorbent, (nanoclay)_x@poly-γ-glutamic acid (γ-PGA)/polyethyleneimine (PEI) hydrogel adsorbent (denoted as N_xPP, x = 0, 20, 40, 60, and 80), for the efficient removal of heavy metal ions (Cu²⁺, Fe³⁺, and Zn²⁺) and organic dyes (Methylene blue, as a typical example) from wastewater. The hydrogel was prepared using a one-pot method, combining γ-PGA and PEI with varying amounts of nanoclay. The N₈₀PP hydrogel demonstrated exceptional adsorption capacities, achieving 224.37 mg/g for Cu²⁺, 236.60 mg/g for Fe³⁺, and 151.95 mg/g for Zn²⁺ within 30 min, along with 88.18 mg/g for Methylene blue within 5 h. The incorporation of nanoclay significantly enhanced the mechanical properties, with compressive strength reaching 560.49 kPa. The hydrogel exhibited excellent reusability, maintaining high adsorption capacity after five cycles. The adsorption kinetics followed a pseudo-second-order model, and the isotherms fit the Freundlich model, indicating a multilayer adsorption mechanism. This study highlights the potential of N_xPP hydrogels as a versatile and sustainable solution for wastewater treatment. Full article