Adsorption Of Phenol Research Articles

Distillery-Waste-Derived C-SiO2 Catalyst Support Reinforces Phenol Adsorption and Selective Hydrogenation.

Selective hydrogenation of lignin-derived phenolic compounds is an essential process for developing the sustainable chemical industry and reducing dependence on nonrenewable resources. Herein, a composite C-SiO2 material (DGC) was prepared via the stepwise pyrolysis and steam activation of the distiller's grains, a fermentation solid waste from the Baijiu industry. After Ru loading, Ru/DGC was used for the catalytic hydrogenation of phenol to cyclohexanol. Steam activation remarkably increased the hydrophilicity and specific surface area of DGC and introduced oxygen-containing functional groups on the surface of DGC, promoting the adsorption of Ru3+. Furthermore, the steam activation of DGC promoted the graphitization of the carbon matrix and formed Si-H/Si-OH bonds on the SiO2 surface. The benzene ring of phenol interacted with the carbon matrix via π-π stacking, and the hydroxyl group of phenol interacted with SiO2 via hydrogen bonding. The synergistic interactions of phenol at the C-SiO2 interface enhanced phenol adsorption to promote the hydrogenation. Consequently, 100% of phenol was hydrogenated to cyclohexanol at 60 °C within 30 min. Furthermore, the optimized catalyst exhibited high activity for phenol hydrogenation even after four reuse cycles. The outstanding stability of the catalyst and its requirement for mild reaction conditions favor its large-scale industrial applications.

Roles of lignin in pore development during activation of peach wood

Cellulose, hemicellulose, and lignin are major components in typical woody biomasses. They have varied reaction networks in activation and thus contribute to pore development in different ways. Removal of one component might significantly affect pore characteristics of resulting activated carbon (AC). This was investigated herein by activation of peach wood (PW), delignified peach wood (DLPW), lignin, and a mixture of lignin/DLPW with K2C2O4 at 800 °C. The results disclosed that delignification increased abundance of aliphatic structures relatively and enhanced mass transfer of volatiles and permeability of K2C2O4 through creating voids. These features together intensified cracking reactions in activation of delignified PW, enhancing bio-oil yield (60.9 vs 56.1 % from PW), diminishing production of AC (17.4 vs 20.2 % from PW), promoting pore development (1218.5 versus 1099.4 m2g-1 from PW), enlarging pore size of micropores and creating more mesopores and macropores in AC. This rendered the AC of superior performance for adsorption of phenol. Co-activation of DLPW and lignin suggested that reactions between DLPW-derived volatiles and lignin-derived char formed carbonaceous deposits that filled pores of AC, diminishing overall specific surface area. The characterization of the activation process with in-situ IR technique indicated that more intensive cracking reactions in activation of DLPW even hindered aromatization but facilitated pore development.

Efficient Electrosynthesis of Valuable para-Benzoquinone from Aqueous Phenol on NiRu Hybrid Catalysts.

Electrocatalytic oxidation of aqueous phenol to para-benzoquinone (p-BQ) offers a sustainable approach for both pollutant abatement and value-added chemicals production. However, achieving high phenol conversion and p-BQ yield under neutral conditions remains challenging. Herein, we report a Ni(OH)2-supported Ru nanoparticles (NiRu) hybrid electrocatalyst, which exhibits a superior phenol conversion of 96.5% and an excellent p-BQ yield of 83.4% at pH 7.0, significantly outperforming previously reported electrocatalysts. This exceptional performance benefits from the triple synergistic modulation of the NiRu catalyst, including enhanced phenol adsorption, increased p-BQ desorption, and suppressed oxygen evolution. By coupling a flow electrolyzer with an extraction-distillation separation unit, the simultaneous phenol removal and p-BQ recovery are realized. Additionally, the developed electrocatalytic system with the NiRu/C anode displays good stability, favorable energy consumption, and reduced greenhouse gas emissions for phenol-containing wastewater treatment, demonstrating its potential for practical applications. This work offers a promising strategy for achieving low-carbon emissions in phenol wastewater treatment.

Efficient Electrosynthesis of Valuable para‐Benzoquinone from Aqueous Phenol on NiRu Hybrid Catalysts

Electrocatalytic oxidation of aqueous phenol to para‐benzoquinone (p‐BQ) offers a sustainable approach for both pollutant abatement and value‐added chemicals production. However, achieving high phenol conversion and p‐BQ yield under neutral conditions remains challenging. Herein, we report a Ni(OH)2‐supported Ru nanoparticles (NiRu) hybrid electrocatalyst, which exhibits a superior phenol conversion of 96.5% and an excellent p‐BQ yield of 83.4% at pH 7.0, significantly outperforming previously reported electrocatalysts. This exceptional performance benefits from the triple synergistic modulation of the NiRu catalyst, including enhanced phenol adsorption, increased p‐BQ desorption, and suppressed oxygen evolution. By coupling a flow electrolyzer with an extraction‐distillation separation unit, the simultaneous phenol removal and p‐BQ recovery are realized. Additionally, the developed electrocatalytic system with the NiRu/C anode displays good stability, favorable energy consumption, and reduced greenhouse gas emissions for phenol‐containing wastewater treatment, demonstrating its potential for practical applications. This work offers a promising strategy for achieving low‐carbon emissions in phenol wastewater treatment.

Kinetic and Mechanistic Analysis of Phenol Adsorption on Activated Carbons from Kenaf

Activated carbons were prepared from kenaf (Hibiscus cannabinus L.). Carbonization was carried out at 600 °C for 2 h, and activation was performed using air at 600 °C and using CO2 at 750 °C. The activated carbons obtained were treated with HNO3 and H2SO4. The samples were characterized by their chemical and physical structure. The activated carbons obtained were mainly macroporous, and their structure underwent major changes with the activation method and acid treatment. Activated carbons were alkaline and acid-treated carbons were neutral. They were used for phenol adsorption and a kinetic and mechanistic study of adsorption was carried out. The fit to the pseudo-second order and Elovich models was predominant. The rate-limiting step of the process was determined to be diffusion within the pores, as the experimental data fit the Bangham model. DFT simulation showed that the preferred adsorption position involves π-π stacking and that oxidation enhances this interaction. Furthermore, the simulation showed that the interaction of phenol with oxygenated functional groups depends on the type of functional group.

Kinetic, equilibrium, and thermodynamic aspects of phenol adsorption onto acrylonitrile-divinylbenzene copolymer

Adsorption of phenol onto acrylonitrile-divinylbenzene copolymer (AN-DVB) was comprehensively investigated with the aspect of kinetic, equilibrium, and thermodynamic. The effect of adsorbent dosage, initial concentration, temperature, and pH were studied in batch adsorption process. Maximum phenol adsorption capacity was obtained at neutral pH of phenol solution (6.8), at room temperature (25 °C) and at higher initial concentrations (500 mg/L) as 117 mg/g. After examining two-parameter- and three-parameter-adsorption-isotherm models, experimental data were represented well by using Freundlich adsorption isotherm model at neutral pH. Due to the all possible interactions like hydrogen bonding, π-π stacking and hydrophobic ineractions have different strengths and energetic values, phenol adsorption at neutral pH (6.8) exhibited a heterogeneous multilayer process. On the other hand, Langmuir and BET models well represented the experimental data obtained beyond neutral pH due to the weakening of different interactions, hence, multilayer but more uniform adsorption occurred. Phenol adsorption followed pseudo-second-order kinetic model that shows the surface interactions play significant role on the adsorption rate. Analysis of Boyd's intraparticle and external diffusion kinetic models indicated that in addition to surface interactions, diffusion also controlled the adsorption rate at room temperature. Activation energy was calculated as 92.99 kJ/mol, which shows the strong interaction between phenol and AN-DVB. Adsorption enthalpy change and entropy change was calculated as −25.731 kJ/mol and −0.041 kJ/molK, respectively. Thermodynamic parameters indicated that adsorption process was exothermic and spontaneous in nature.

Development of a natural ingredient based on phenolic compounds from propolis extract and bentonite and its application in carrageenan hydrogels

Nowadays, there is an increasing consumer demand for more natural and environmentally friendly food additives. The current research aimed to produce and characterize a new additive based on bentonite and the phenolic compounds from green propolis extract, as well as to characterize the effect of this additive on the rheological properties of carrageenan hydrogels. The new additive (biohybrid) was obtained after the adsorption of phenolic compounds on the clay platelets. The adsorption mechanism was explained by Langmuir and Freundlich models, which suggested that adsorbed phenolic compounds form a monolayer and multilayers on the clay surface. Despite phenolic adsorption, the physico-chemical attributes of the bentonite remained unchanged. The incorporation of the biohybrid (BH) increased the sol-gel transition temperature of carrageenan hydrogels. This research reports for the first time the development and application of a new natural ingredient with potential food applications.

Inherent water in green pine needles and cypress leaves induces self-activation in microwave pyrolysis

The response of water to microwaves creates the possibility of activating green waste for the generation of porous biochar with inherent water. This hypothesis is verified herein through the microwave pyrolysis of green and dried pine needles and cypress leaves at 500 to 800 °C. The results indicate that the inherent water in the green samples induce steam reforming or gasification, thereby forming more gases at the expense of biochar and organics, such as light and heavy phenolics in bio-oil. The intensive gasification induced by the inherent water of green pine needles effectively promotes the pore development of biochar at 800 °C (805.9 versus 360.4 m2/g from the dried sample) and the adsorption of phenol (50.3 versus 34.8 mg/g from the dried sample). A similar result is observed for the pyrolysis of cypress leaves at 800 °C (452.1 m2/g from the green samples versus 110.8 m2/g from the dried samples). A lower temperature (i.e., 500 °C) with insufficient gasification results in no marked difference in pore development. Accelerated gasification with steam leads to the excessive removal of aliphatic organics but also introduces more oxygen in the biochar, making it more hydrophilic with a more fragmented surface. Nevertheless, potential local hot spots, if any, do not lead to the decomposition of inorganics, such as CaCO3, in the pyrolysis of green samples, while the pyrolysis of dried cypress does. The pyrolysis in in-situ infrared shows that 500 °C is required to effectively destruct hydrogen bonds in the green samples and the inherent water promotes the formation of more oxygen-containing functionalities but not aromatization.

Co–Fe/Al2O3 catalyst for low-temperature steam reforming of phenol for hydrogen production

In this study, a series of high-efficient catalyst, Co–Fe/Al2O3, were synthesized via the sol-gel method for low-temperature phenol steam reforming (PSR). The optimized catalyst, 15Co–2Fe/Al2O3, exhibited a remarkable phenol conversion of 95.3%, a H2 yield of 92.1% at 450 °C, GHSV = 7500 h−1 and a steam-to-carbon (S/C) ratio of 10. Furthermore, the catalyst activity was maintained for 660 min before a gradual decline was observed. The NH3-TPD analysis revealed that the addition of Fe enhanced the surface acidity of the catalyst, providing more active sites for phenol adsorption and activation. This study aims to address the challenges associated with high reaction temperatures and poor catalyst stability in PSR. Various characterization techniques have been employed to investigate the reaction mechanisms of bimetallic catalysts in low-temperature PSR.

Development and application of metal–organic frameworks and spherical carbon particles for efficient recovery of phenols and oils from coal chemical wastewater: A new full-process adsorption treatment mode

To address the challenges of high energy consumption and low efficiency in recovering phenols and oils from coal chemical wastewater (CCW), this study focused on the design and synthesis of metal–organic frameworks and spherical carbon particle (MOFs/SCP) adsorbents with a high adsorption capacity and ease of desorption. Additionally, a new comprehensive treatment mode named “adsorption-desorption-regeneration-recovery” (ADRR) was developed to efficiently recover phenols and oils from CCW. The results revealed that the ADRR treatment mode maintained high adsorption and desorption efficiencies of MOFs/SCP, which remained consistently above 95 %. Additionally, methanol regeneration reached ∼ 90 %, and the recovery efficiency of phenols and oils was ∼ 83 %. The analysis of the adsorption behavior model indicated that the adsorption of phenols and oils by MOFs/SCP mainly involved monolayer chemical adsorption characterized by spontaneity, heat absorption, and disorder. The dynamic adsorption model exhibited a strong correlative ability to predict and assess the adsorption capacity, rate, equilibrium, and operating parameters. Finally, structural analyses and molecular dynamics simulations revealed that the micro-interaction mechanisms between MOFs/SCP and phenols and oils mainly depended on the distinctive hydrophobic nature and porous adsorption capabilities of MOFs/SCP. These interactions were mainly facilitated by electrostatic interactions, π–π interactions, and hydrogen bonding. The findings of the study are crucial for achieving high-value recovery of phenols and oils from CCW and, promoting the clean and sustainable growth of the coal chemical industry.

Regulating the electronic state of Pd nanoclusters and Lewis acid density by the carbon doping for synergistically enhancing phenol hydrogenation in green solvent

Pd-based catalysts have been widely applied in selective hydrogenation of phenol. However, avoiding excessive hydrogenation of C=O functional groups is still challenging. Here, we synthesized Pd nanoclusters supported by N-doped C-Al2O3 (Pd/CN-Al2O3) catalyst for phenol hydrogenation. Remarkably, the cyclohexanone yield shows a volcano trend with the doping of carbon content, where Pd/CN-Al2O3 with carbon content of 6.76 % (Pd/CN-Al2O3-2) exhibits the highest cyclohexanone yield. Under the optimized conditions, the phenol conversion and cyclohexanone selectivity over Pd/CN-Al2O3-2 are 99.5 % and 96.7 %, respectively. The corresponding TOF value is 1731.7 h−1, which is 5.8 times higher than that of Pd/Al2O3 (299.7 h−1). Mechanism studies reveal the excellent catalytic performance of Pd/CN-Al2O3-2 is mainly attributed to the synergistic effect of electron-deficient Pd clusters and Lewis acid sites. Pd nanoclusters with moderate electron-deficient state and moderate Lewis acid density are beneficial to the adsorption of phenol and the desorption of cyclohexanone, thereby exhibiting the best phenol conversion and cyclohexanone selectivity. This work provides a carbon modification strategy to regulate the structure of Pd-based catalysts, which is a helpful guide for the hydrogenation reactions.

Green synthesis of zinc oxide nanoparticles for the removal of phenol from textile wastewater

This study investigated the use of zinc oxide nanoparticles (ZnO NPs) as an adsorbent for removing total phenols from textile wastewater. The ZnO NPs were synthesized by reducing Zn(NO3)2⋅6H2O using an extract from Neem leaves (Azadirachta indica). Characterization of the adsorbent was performed using Fourier Transform Infrared (FTIR) spectroscopy to identify functional group modifications, high-resolution scanning electron microscopy (HRSEM) for structural orientation, energy dispersive spectroscopy (EDS) for elemental analysis, and X-Ray diffraction analysis (XRD) for crystallinity, revealing particle crystallinity around 200 nm. Adsorption experiments were conducted over contact times of 20–60 min, with adsorbent loadings between 0.2 and 1 g/100 mL, and temperatures ranging from 30 to 50 °C. Optimal phenol removal, achieving 55.93% (0.67 mg/L), occurred at 43.40 min, 33.70 °C, and an adsorbent dosage of 0.69 g/L of textile wastewater. The phenol adsorption process using ZnO NPs was exothermic, spontaneous, and required low energy, fitting well with the Langmuir isotherm and following a pseudo-second-order kinetic model.

Evaluation of reduced graphene oxide from cotton waste as an efficient phenol adsorbent in aqueous media.

The elimination of organic substances, such as phenol, in conventional and biological processes, has been considered a challenge for the petroleum industry. In this work, reduced graphene oxide (rGO), obtained from cellulosic biomass (CB-rGO), as cotton waste, was employed as a phenol adsorbent in an aqueous solution simulating refinery effluent. The CB-rGO was characterized using HRTEM, Raman, XRD, FTIR, BET, and zeta analysis. The behavior of variables such as pH, contact time, temperature, CB-rGO mass, and adsorbate concentration on the characteristics of the adsorption process were continuously investigated. These parameters of the adsorption process were evaluated across a range of adsorbent concentrations from 100 to 300mg/L, pH in the range of 2-11, adsorbent mass 5-25mg, contact time of 0-180min, and temperature of 20-60°C. The adsorption isotherm data were better described by the Freundlich equation compared to the Langmuir and Sips models, despite the small difference in R2 values. Mechanism diffusion was analyzed using the Boyd model and confirmed to be the rate-limiting step in the adsorption process. The endothermic nature of this CB-rGO adsorption process with phenol was confirmed by verifying the thermodynamic data. This successful removal of phenol from synthetic effluents highlights the promising potential of this adsorbent obtained from an industrial residue and being an ecologically more sustainable alternative compared to the synthesis of other materials identified to remove this contaminant.

D/A heterojunction photocatalysts interspersed onto biochar to couple photocatalysis and adsorption for visible light-responsive efficient removal of pollutants

Phenol has various applications in industry, due to its hazardousness, solubility, and volatility, it persists in water and poses a risk to human health. People are excited by the progress of photodegradation technology that facilitates water pollution treatment. The effect of side-chain engineering is proven to enhance photodegradation performance by improving optoelectronic properties. Therefore, here is a strategy that introduces functional groups to change the electron cloud density, achieving excellent optoelectronic properties evidenced by efficient exciton dissociation, separation, and fine-tuned energy level. Subsequently, by coupling of photocatalysis and adsorption, the donor/acceptor (D/A) heterojunction photocatalysts (PBDB-T: BTTIC-TT, PBDB-T: BTTIC-Ph) are designed via loading on coconut-shell carbon to process phenol. The results indicate that the champion photocatalyst PBDB-T: BTTIC-TT possesses superior optoelectronic properties, which can be attributed to the stronger electron-withdrawing ability of thieno[3,2-b]thiophene than benzene. Consequently, the synergistic efficiency of adsorption and photocatalysis of phenol (10, 20 mg/L) are removed within 10 mins over 90 % which is still valid after twenty cycles. Surprisingly, a high concentration of phenol (100 mg/L) also exhibited excellent removal efficiency of over 80 % within 60 min.

Impact of Thermally Inactivated Non-Saccharomyces Yeast Derivatives on White Wine.

While a recent characterization of non-Saccharomyces thermally inactivated yeasts (TIYs) in a wine-like solution highlighted the release of oenologically relevant compounds and different oxygen consumption rates and antioxidant activity, here the impact of TIYs derived from Saccharomycodes ludwigii (SL), Metschnikowia pulcherrima (MP), Torulaspora delbrueckii (TD), and Saccharomyces cerevisiae (SC), as the reference strain, was evaluated in white wine. Wine treatment with TIYs resulted in an increase in polysaccharide concentration compared to the untreated wine, with SL-TIY exhibiting the highest release. Additionally, all TIYs, particularly SL-TIY, improved protein stability by reducing heat-induced haze formation. The addition of TIYs also demonstrated an effect on color parameters through phenolic compound adsorption, preventing potential browning phenomena. All TIYs significantly impacted the wine's volatile profile. Overall, it was shown that an improvement in wine quality and stability may be obtained by using TIYs in the winemaking process.

Direct activation of petroleum pitch-based mesoporous carbon for phenol adsorption

Phenol, a highly toxic substance that poses a serious threat to both environment and human, is difficult to degrade. Adsorption using porous adsorbents is an effective method for the removal of phenol from water. Herein, petroleum pitch-based mesoporous carbons (PPMCs) were prepared using magnesium citrate as a template and then PPMCs were used for the adsorption of phenol in water. By activating petroleum pitch at 900 ℃ with a mass ratio of MgO to petroleum pitch of 4:1, a mesoporous carbon (PPMC-4–900) with abundant mesopores (high specific area of 1627 m2·g−1 and pore volume of 1.81 cm3·g−1) was obtained. The phenol adsorption capacity of PPMC-4–900 reaches up to 189.96 mg·g−1. The adsorption behavior of phenol on PPMCs followed Freundlich model, indicating it is multilayer adsorption on PPMCs. The adsorption kinetics of phenol on PPMCs are consistent with pseudo-first-order adsorption and pseudo-second-order adsorption model, suggesting the adsorption process of phenol on PPMC-4–900 is not only influenced by physical adsorption but also controlled by chemical adsorption. And the thermodynamic parameters indicate that the adsorption process is spontaneous and exothermic. Furthermore, the PPMCs exhibited excellent recyclability (recovery rate of adsorption capacity over 91 %) after five adsorption/desorption cycles. These results reveal that PPMCs are a promising adsorbent for phenol removal from water.

Reusable biochars derived from Camellia oleifera shell via K2CO3 activated for phenol-enhanced adsorption

Porous biochar materials (BC) have shown excellent performance in energy storage and water treatment adsorption. Carbonization of agricultural and forestry solid waste and fixation in the form of stable biochar to form biochar materials can achieve green "waste utilization for treatment wastewater". In this study, BC samples were generated by using Camellia oleifera shell (COS) as raw material and K2CO3 as green activator in-situ pyrolysis. The adsorption behavior of COS biochar in aqueous solution was evaluated using phenol as a pollutant probe. The synergistic effect of pyrolysis temperature and K2CO3 activation promoted the development of the pore structure of BC. The X-ray photoelectron spectroscopy results indicated that K2CO3 activation promoted the formation of C-C defects and promoted phenol adsorption. KBC-900 exhibited superior absorption capacity for phenol (300.15 mg/g). The activation of K2CO3 also promoted the adsorption of oxygen. In addition, using H2O2 for regenerating biochar did not show a significant decrease in the adsorption rate after five cycles (decline rate < 5 %). The strong adsorption capacity of KBC-900 for phenol might be due to the presence of π-π interactions, hydrogen bonds, and van der Waals interactions during the adsorption process.

Performance of zero-valent iron immobilized on activated carbon cloth for the removal of phenol from wastewater

BackgroundDischarge of large amounts of untreated industrial effluent into water bodies pose significant environmental challenges worldwide. This is due to the limitations of traditional wastewater treatment methods in the treatment of recalcitrant organic pollutants. Fenton processes involves the generation of hydroxyl radicals that are well suited to degrade organics in effluent water. This study focuses on reducing slag generation during Fenton processes and enhancing the reuse of nano-zero-valent iron (NZVI) through the immobilization of NZVI on activated carbon cloth (ACC) through a chitosan (CH) linker with phenol as a model pollutant.ResultsMicrostructural and spectroscopic techniques were employed to study the materials prepared and 37.5 wt% iron loading was achieved. Phenol degradation of 96.3% at 40 °C at pH of 3.0 with 50 mM H2O2 was achieved using ACC-CH-NZVI. Adsorption and degradation studies carried out using ACC-CH-NZVI catalyst revealed that phenol adsorption onto ACC-CH-NZVI fits the Langmuir isotherm model, following the pseudo-second-order kinetic model and first-order reaction kinetics. Thermodynamic studies indicate the non-spontaneous, endothermic and irreversible nature of the removal process. Comparing ACC-CH-NZVI with ACC and ACC-CH, phenol removal using ACC drops from 87.8 to 39%, while using ACC-CH, the removal efficiency drops from 73 to 20.9% and using ACC-CH-NZVI, phenol removal drops from 96.3 to about 70% and total organic carbon removal drops from 79 to about 60% with minimal iron leaching, highlighting the superior performance of ACC-CH-ZVI and the role of NZVI in enhancing phenol removal.ConclusionsThe catalyst demonstrated good stability for phenol degradation to about 70% phenol removal from simulated wastewater and 60% TOC removal from industrial wastewater after five treatment cycles with minimal Fe leaching.Graphical abstract

Construction of coal fly ash-based spherical grain adsorbents and their adsorption characteristics on phenolic compounds

Addressing the significant emissions and severe pollution hazards posed by coal fly ash waste in the coal chemical industry, as well as the challenges in recovering phenolic substances from coal chemical wastewater, this study utilized coal fly ash as a raw material to construct two types of spherical grain adsorbents: coal fly ash and coal gangue spherical grain (CFAGsg) and coal fly ash and pyrite spherical grain (CFAPsg). The adsorption performance of CFAGsg and CFAPsg towards phenolic substances in coal chemical wastewater was investigated. The research results demonstrated that CFAGsg and CFAPsg exhibited adsorption capacities of 20.31 mg/L and 30.42 mg/L for phenol, respectively, and maintained stable adsorption performance even after multiple regeneration cycles. Further analysis using kinetic, isotherm, and thermodynamic models, along with various characterization techniques, revealed that the adsorption of phenol onto CFAGsg and CFAPsg was primarily governed by physical and chemical adsorption, involving an endothermic reaction. Moreover, the study on the adsorption mechanism of phenol revealed that the adsorption behavior of CFAGsg and CFAPsg was mainly driven by pore filling, π-π stacking, and hydrogen bonding. Additionally, hydrophobic interactions were involved in the adsorption of phenol onto CFAGsg, while surface complexation forces played a role in the adsorption of phenol onto CFAPsg. Overall, the research findings provide vital theoretical support and practical application prospects for the high-value utilization of coal fly ash and the clean production of the coal chemical industry.

Optimization and mechanistic insight of phenol removal using an effective green kaolin adsorbent through experimental and computational approaches

The discharge of phenols into the aquatic environment has detrimentally affected human health and the aquatic ecosystem. Hence, removing phenols from polluted water bodies has been a global concern. In this study, a natural and low-cost adsorbent, kaolin, was used to remove phenol from aqueous solutions. Experimental and computational approaches were applied to optimize the removal efficiency and provide mechanistic insight into the phenol removal process. Based on the response surface methodology findings, the optimum conditions were pH 1.6, 40 min, 50 mg/L, and 2 g with 92.19 % maximum percentage removal. The regeneration test shows that kaolin retained over 76.76 % of adsorption capacities. SEM and FESEM reveals the surface morphology and effectiveness of kaolin as phenol removal. The best fit for the Isotherm adsorption for the phenol on kaolin is Freundlich isotherm, which indicated multilayer adsorption. The hydroxyl group from phenol (-OH) and the siloxane group of kaolin (Si-O-Si) shifted, suggesting the presence of a hydrogen bond between kaolin and phenol during adsorption, as determined by one- and two-dimensional IR spectroscopy. Density functional theory calculations were used to support the experimental results by providing information on the Mulliken charge and electronic transition of the complex to improve understanding of the adsorption of phenol on kaolin. Based on the quantum theory of atoms in molecules analysis (QTAIM) and the reduced density gradient non-covalent interaction (RDG-NCI) technique, the chemical reaction occurring during the removal of phenol by kaolin was determined to occur through hydrogen bonding and classified as an intermediate type (∇2ρ(r) > 0 and H < 0). Further characterizations employing molecular electrostatic potential, global reactivity, and local reactivity descriptors were conducted to investigate the mechanism of the phenol adsorption on kaolin. The findings demonstrated that phenol functions as an electrophile while kaolin acts as a nucleophile during the formation of hydrogen bonds, where the interaction occurred between the O2 atom of kaolin (electron donor) and the H13 atom of phenol (electron acceptor).