Upcycling olive oil cake through wet torrefaction to produce hydrochar for water decontamination

Tetraethylenepentamine-Grafted Amino Terephthalic Acid-Modified Activated Carbon as a Novel Adsorbent for Efficient Removal of Toxic Pb(II) from Water

In this study, a new composite, tetraethylenepentamine (TEPA), was incorporated into amino terephthalic acid-modified activated carbon (ATA@AC) through a one-pot integration of TEPA with the COOH moiety of ATA@AC. This process resulted in the creation of a TEPA@ATA@AC composite for Pb(II) removal from an aquatic environment. Several techniques, including SEM, EDX, FT-IR, TGA, XRD, and Zeta potential, were employed to emphasize the chemical composition, morphology, and thermal durability of the as-synthesized TEPA@ATA@AC composite. The impact of experimental variables on the adsorption of Pb(II) ions was studied using batch adsorption. The uptake assessment suggested that the TEPA@ATA@AC composite exhibited superior Pb(II) removal performance with high removal efficiency (97.65%) at pH = 6.5, dosage = 0.02 g, equilibrium time = 300 min, and temperature = 298 K. The isotherm data exhibited good conformity with the Langmuir isotherm model, whereas the kinetics data displayed strong agreement with both pseudo-first-order and pseudo-second-order kinetics models. This reflected that the Pb((II) uptake by the TEPA@ATA@AC composite was caused by physisorption coupled with limited chemisorption. The greatest monolayer uptake capacity of the TEPA@ATA@AC composite was 432.8 mg/g. The thermodynamic findings indicated that the Pb(II) uptake on the TEPA@ATA@AC composite was an exothermic and feasible process. After five adsorption-desorption runs, the TEPA@ATA@AC composite maintained a superior uptake capacity (83.80%). In summary, the TEPA@ATA@AC composite shows promise as a potent adsorbent for effectively removing Cr(VI) from contaminated water, with impressive removal efficiency.

Optimization of two-phase synthesis of Fe-hydrochar for arsenic removal from drinking water: Effect of temperature and Fe concentration

Arsenic-contaminated water is a global concern that demands the development of cost-effective treatments to ensure a safe drinking water supply for people worldwide. In this paper, we report the optimization of a two-phase synthesis for producing a hydrochar core from olive pomace to serve as support for the deposition of Fe-hydroxide, which is the active component in As(V) removal. The operating conditions considered were the initial concentration of Fe in solution in the hydrothermal treatment (phase I) and the temperature of Fe precipitation (phase II). The obtained samples were characterized for their elemental composition, solid yield, mineral content (Fe and K), phenol release, As(V) sorption capacity, and sorbent stability. Correlation analysis revealed that higher Fe concentrations (26.8 g/L) ensured better carbonization during hydrothermal treatment, increased arsenic removal, reduced concentrations of phenols in the final liquid, and improved stability of the sorbent composite. On the other hand, the temperature during Fe precipitation (phase II) can be maintained at lower levels (25-80 °C) since higher temperatures yielded lower adsorption capacity. Regression analysis demonstrated the significance of the main effects of the parameters on sorption capacity and provided a model for selecting operating conditions (Fe concentration and phase II temperature) to obtain composite sorbents with tailored sorption properties.

Nigella sativa-Manganese Ferrite-Reduced Graphene Oxide-Based Nanomaterial: A Novel Adsorbent for Water Treatment

In this study, a novel nanohybrid composite was fabricated via the incorporation of manganese ferrite (MnFe2O4) nanoparticles into the integrated surface of reduced graphene oxide (rGO) and black cumin seeds (BC). The nanohybrid composite was prepared by a simple co-precipitation method and characterized by several spectroscopic and microscopic techniques. The characterization analysis revealed that the rGO-BC surface was decorated with the MnFe2O4. The strong chemical interaction (via electrostatic and H-bonding) between the integrated surface of rGO-BC and MnFe2O4 nanoparticles has been reported. The prepared composite was highly porous with a heterogeneous surface. The average size of the prepared composite was reported in the ranges of 2.6-7.0 nm. The specific surface area of the prepared composite was calculated to be 50.3 m2/g with a pore volume of 0.061 cc/g and a half pore width of 8.4 Å. As well, many functional sites on the nanohybrid composite surface were also found. This results in the excellent adsorption properties of nanohybrid composite and the effectual elimination of methylene blue dye from water. The nanohybrid was tested for various linear isotherms, such as Langmuir and Freundlich, for the adsorption of methylene blue dye. The Freundlich isotherm was the well-fitted model, proving the adsorption is multilayer. The maximum Langmuir adsorption capacity of nanohybrid composite for methylene blue was reported to be 74.627 mg/g at 27 °C. The adsorption kinetics followed the pseudo-second-order recommended surface interaction between the dye and nanohybrid composite. The interaction between methylene blue and the nanohybrid composite was also confirmed from the FTIR spectrum of the methylene blue-loaded adsorbent. The rate-determining step for the present study was intraparticle diffusion. Temperature-dependent studies of methylene blue adsorption were also carried out to estimate adsorption's free energy, enthalpy, and entropy. The methylene blue adsorption was feasible, spontaneous, and endothermic. A comparison study revealed that the present materials could be successfully prepared and used for wastewater treatment.

Cassava bagasse as an alternative biosorbent to uptake methylene blue environmental pollutant from water

Herein, the methylene blue (MB) biosorption from the agroindustrial residue (cassava bagasse) is reported. The cassava bagasse residue presented an irregular surface, anionic character, and low specific surface area. The experiments were performed in batch mode. The biosorption behavior was investigated through the experimental variables, initial concentration of MB, pH, and temperature. The maximum biosorption capacity (170.13 mg g^-1) reached 328 K and pH 10.0. The equilibrium and kinetics were better fitted by the Sips and general order (R² ≥ 0.997 and R²_adj ≥ 0.996) models, respectively. Furthermore, the thermodynamic study revealed a spontaneous (ΔG⁰ < 0) and endothermic process. Finally, the results showed cassava bagasse is a potential material for biosorption dyes from the aqueous medium. In addition, the biosorbent has a low aggregate cost and high availability, which contributes to the destination of large amounts of waste and inspires engineering applications.

Multifunctional Loblolly Pine-Derived Superactivated Hydrochar: Effect of Hydrothermal Carbonization on Hydrogen and Electron Storage with Carbon Dioxide and Dye Removal

Pore modulation via hydrothermal carbonization (HTC) needs investigation due to its crucial effect on surface that influences its multirole utilization of such ultraporous sorbents in applications of energy storage- hydrogen and capacitive- as well as for pollutant abatement- carbon capture and dye removal. Hence, loblolly pine was hydrothermally carbonized followed by KOH activation to synthesize superactivated hydrochars (SAH). The resulting SAHs had specific surface area (SSA) 1462-1703 m²/g, total pore (TPV) and micropore volume (MPV) of 0.62-0.78 cm³/g and 0.33-0.49 cm³/g, respectively. The SAHs exhibit excellent multifunctional performance with remarkably high atmospheric CO₂ capture of 145.2 mg/g and high pressure cryogenic H₂ storage of 54.9 mg/g. The fabricated supercapacitor displayed substantial specific capacitance value of maximum 47.2 Fg^-1 at 1 A g^-1 in 6 M KOH and highest MB dye removal of 719.4 mg/g. Higher HTC temperature resulted in increased surface porosity as higher SSA, TPV benefitted H₂ storage and MB dye removal while superior MPV favored CO₂ capture. Moderate HTC temperature ensured higher mesopore-to-macropore volume ratio favoring electrochemical performance. Isotherm modelling of the adsorbates was compared using models: Langmuir, Freundlich, Langmuir- Freundlich and Temkin.

NaOH-assisted H2O2 post-modification as a novel approach to enhance adsorption capacity of residual coffee waste biochars toward radioactive strontium: Experimental and theoretical studies

In this study, NaOH-assisted H₂O₂ post-modification was proposed as a novel strategy to enhance the adsorption of radioactive strontium (Sr) onto residual coffee waste biochars (RCWBs). To validate its viability, the adsorption capacities and mechanisms of Sr(II) using pristine (RCWB_P), H₂O₂ post-modified (RCWB_HP), and NaOH-assisted H₂O₂ post-modified residual coffee waste biochars (RCWB_NHP) were experimentally and theoretically investigated. The highest adsorption capacity of Sr(II) for RCWB_NHP (10.91 mg/g) compared to RCWB_HP (5.57 mg/g) and RCWB_P (5.07 mg/g) was primarily attributed to higher negative surface zeta potential (RCWB_NHP = -5.66 → -30.97 mV; RCWB_HP = -0.31 → -11.29 mV; RCWB_P = 1.90 → -10.40 mV) and decoration of Na on the surfaces of RCWB_P via NaOH-assisted H₂O₂ post-modification. These findings agree entirely with the theoretical observations that the adsorption of Sr(II) onto RCWB_P and RCWB_HP was controlled by electrostatic interactions involving carbonyls whereas enriched carboxylic acids and decorated Na on the surfaces of RCWB_NHP through the replacement of Mg and K by NaOH-assisted H₂O₂ modification stimulated electrostatic interactions and cation exchanges governing the adsorption of Sr(II). Hence, NaOH-assisted H₂O₂ post-modification seemed to be practically applicable for improving the adsorption capacity of Sr(II) using RCWB-based carbonaceous adsorbents in real water matrices.

Efficient removal of Remazol Brilliant Blue R from water by a cellulose-based activated carbon

Due to its wide application and high toxicity, Remazol Brilliant Blue R (RBBR) has become a fatal contaminate in aquatic environment. In this study, to remove RBBR, a cellulose-based activated carbon (CAC) was synthesized at 800 °C with a cellulose-based hydrocarbon (CHC) activated by NaOH. The CHC was synthesized by the hydrothermal method with microcrystalline cellulose and urea as raw materials. The CAC possessed great amounts of N and O-containing functional groups and had well-developed pore structure. The BET specific surface area of CAC reached up to 1872.30 m²/g. The maximum adsorption capacity of CAC on RBBR was 653.19 mg/g during which chemical adsorption was the dominant mechanism. Adsorption thermodynamics indicated that the adsorption of RBBR by CAC was exothermic and spontaneous. Regeneration adsorption and ion competition experiments showed that the material could be used repeatedly and had good anti-interference ability. In addition, the removal rates of RBBR by CAC in actual water bodies, including river water and artificial lake water, were above 99.40%. Therefore, the novel CAC shows great potential for the remediation of printing and dyeing wastewater.

Simultaneous co-hydrothermal carbonization and chemical activation of food wastes to develop hydrochar for aquatic environmental remediation

Locally generated food wastes, such as Arabic coffee ground (ACG) and olive oil cake (OOC) were converted to N-ACG: OOC - 3 hydrochar (HC) through simultaneous co-hydrothermal carbonization (Co-HTC) and chemical activation. The optimized ACG: OOC mass ratio (g: g) and chemical activation agent used were 1.2: 0.8 and 0.1 M HNO₃, respectively. Spectroscopic analyses confirmed the dominance of oxygen-containing functionalities, whereas the X-ray diffraction pattern displayed peaks for both sucrose and cellulose on N-ACG: OOC - 3. The developed HC was tested for methylene blue (MB) and crystal violet (CV) adsorption in aqueous systems. Batch scale adsorption studies showed pH, initial concentration (C_o), time (t), and temperature (T) dependent dye uptake. Maximum dye uptake was observed at pH 7, with 50 - 70% and 76 - 90 % CV and MB removal achieved within 15 min at varied C_o: 50 - 200 mg/L. Adsorption was governed by multiple mechanisms, including hydrogen bonding, electrostatic interactions, π-π interactions, and n-π interactions. Dye elution was higher in ethanol (EtOH: C₂H₅OH), and CV elution (50.8%) was more significant than MB elution (14.8%).

Adsorption of Methylene Blue by Biosorption on Alkali-Treated Solanum incanum: Isotherms, Equilibrium and Mechanism

In this study, a new bio-adsorbent (NASIF) was successfully prepared via chemical activation of Solanum incanum (SI) with hydrogen peroxide and sodium hydroxide reagents as an inexpensive and effective adsorbent for the removal of methylene blue (MB) from aqueous media. The morphology of the NASIF adsorbent surface and the nature of the potential MB interactions were examined by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) micrograph. FTIR results suggested that carboxyl, carbonyl, and hydroxyl groups were involved in MB adsorption on the NASIF surface. EDX analysis confirmed the successful increase of oxygen-containing functional groups during the chemical activation. The influence of important factors was studied using the batch method. The results revealed that the maximum removal efficiency was 98% at contact time: 120 min; pH: 6.5, adsorbent dose: 40 mg; and temperature-25 °C. Isothermal behavior was evaluated using three non-linear isotherm models, Langmuir, Freundlich, and D–R isotherm. MB adsorption onto NASIF adsorbent followed the Langmuir isotherm model with maximum monolayer capacity (mg/g) at 25 °C. Meanwhile, the PSO kinetics model was found to be better than PFO kinetic model for describing the adsorption process using kinetic models. Based on the D–R model, the free energy (E, kJ mol−1) values were in the range of 0.090–0.1812 kJ mol−1, which indicated that the MB adsorption onto NASIF may belong to physical adsorption. The adsorption mechanism of MB onto NASIF adsorbent mainly includes electrostatic attraction, π-π interaction, n-π interaction, and H-bonding. The thermodynamic parameters revealed that the adsorption process was a feasibility, spontaneous and exothermic process. Finally, the result of the present work could provide strong evidence of the potential of NASIF adsorbent for eliminating MB from aqueous media.

Pyrolysis of mustard oil residue: A kinetic and thermodynamic study

Critical analysis of thermogravimetric data, characterization of the biomass, and kinetic and thermodynamic analyses are crucial in the design of efficient biomass pyrolysis systems. In this study, characterization, kinetic and thermodynamic analysis was performed for pyrolysis of mustard oil residue (MOR). Thermogravimetric analysis (TGA) with differential thermal analysis (DTA) was applied to study thermal decomposition behaviour of MOR at 10, 20, and 30 °C/min. FTIR and XRD analyses were used to characterize MOR. Average activation energy estimated from employed isoconversional methods was ≈155 kJ/mol. Variation in activation energy was found to be statistically insignificant as suggested by p-value of 0.992 by one-way ANOVA method. The pyrolytic temperature for MOR ranged from 234 to 417 °C. Reaction mechanism predicted as R3 (third order) and D3 (three dimensional). Thermodynamic parameters (ΔH_α, ΔG_α, and ΔS_α) showed that endothermicity increased from 0.2 to 0.8 conversion and product had highest energy at 0.8 conversion.

A Comparative Study on Hexavalent Chromium Adsorption onto Chitosan and Chitosan-Based Composites

Chitosan (Cs)-based composites were developed by incorporating silica (Cs-Si), and both silica and hydroxyapatite (Cs-Si-Hap), comparatively tested to sequester hexavalent (Cr(VI)) ions from water. XRD and FT-IR data affirmed the formation of Cs-Si and Cs-Si-Hap composite. Morphological images exhibits homogeneous Cs-Si surface, decorated with SiO2 nanoparticles, while the Cs-Si-Hap surface was non-homogeneous with microstructures, having SiO2 and Hap nanoparticles. Thermal analysis data revealed excellent thermal stability of the developed composites. Significant influence of pH, adsorbent dose, contact time, temperature, and coexisting anions on Cr(VI) adsorption onto composites was observed. Maximum Cr(VI) uptakes on Cs and developed composites were observed at pH 3. The equilibration time for Cr(VI) adsorption on Cs-Si-Hap was 10 min, comparatively better than Cs and Cs-Si. The adsorption data was fitted to pseudo-second-order kinetic and Langmuir isotherm models with respective maximum monolayer adsorption capacities (qm) of 55.5, 64.4, and 212.8 mg/g for Cs, Cs-Si, and Cs-Si-Hap. Regeneration studies showed that composites could be used for three consecutive cycles without losing their adsorption potential.

Biochars derived from bamboo and rice straw for sorption of basic red dyes

The primary purpose of this study is to eliminate Basic Red 46 dye from aqueous solutions utilizing batch experiments by adsorption on biochars prepared from bamboo and rice straw biomass. Biochars prepared from bamboo (B), and rice straw (R) was pyrolyzed at 500°C (B500 and R500). Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR) Spectroscopy, X-ray Diffraction (XRD), and surface area and porosity analyzers were used to characterize the B500 and R500 samples. The characterization results indicated that the biochars possessed an amorphous porous structure with many functional groups consisting primarily of silicates. The adsorption rate of BR46 was evaluated using two kinetic models (pseudo-first-order and pseudo-second-order), and the results indicated that the pseudo-second-order model fitted to the experimental data well (R2>0.99). Nearly 24 h was sufficient to achieve equilibrium with the dye adsorption for the two biochars. R500 had a greater adsorption efficiency than B500. As pH levels increased, the dye's adsorption capability increased as well. The Langmuir and Freundlich isotherm models were used to investigate the equilibrium behavior of BR46 adsorption, and the equilibrium data fitted well with the Langmuir model (R2>0.99) compared to the Freundlich model (R2>0.89). The maximum adsorption capacities of BR46 are 9.06 mg/g for B500 and 22.12 mg/g for R500, respectively. Additionally, adsorption capacity increased as temperature increased, indicating that adsorption is favored at higher temperatures. The electrostatic interaction is shown to be the dominant mechanism of BR46 adsorption, and BR46 acts as an electron-acceptor, contributing to n-π EDA (Electron Donor-Acceptor) interaction. Thermodynamic parameters for the dye-adsorbent system revealed that the adsorption process is spontaneous and feasible. The values of the adsorption coefficient (Kd) were on the order of 102-103. Kd of R500 was greater than that of B500, indicating that R500 had a greater adsorption capacity. The results showed that R500 could be used as a low-cost alternative adsorbent for removing BR46 from effluents.