Adsorption Of Phenol Research Articles

Development of sunflower seed hulls crosslinked β-cyclodextrin (SFSH-β-CD) composite materials for green adsorption of phenol and naphthenic acid

Development of sunflower seed hulls crosslinked β-cyclodextrin (SFSH-β-CD) composite materials for green adsorption of phenol and naphthenic acid

Hydrophobic deep eutectic solvent-impregnated sponge for efficient phenol adsorption from aqueous media

Hydrophobic deep eutectic solvent-impregnated sponge for efficient phenol adsorption from aqueous media

Sonochemically Modified Lapindo Mud Using Sulfuric Acid for Efficient Adsorption of Phenol in Aqueous Media and Real Wastewater Samples

Pharmaceutical industrial wastewater frequently contains high amounts of phenolic substances, which pose severe threats to the ecosystem and human health. Therefore, efficient removal of these pollutants is urgently needed. In the present work, sulfated Lapindo mud (SLM) was prepared using the sonochemical method and applied as an adsorbent for phenol removal in aqueous media and actual wastewater samples from Code River, Yogyakarta. Modification of Lapindo mud (LM) using sulfuric acid enables it to remove its impurities, resulting in a material containing 78.4% silica (SiO2) and 15.3% alumina (Al2O3). The SLM adsorbent demonstrated sufficient adsorption performance of 49.8% with an optimal initial phenol concentration of 120 mg/L with a contact time of 100 min at pH of 10. The maximum adsorption capacity (qmax) obtained by the Langmuir isotherm model was 27.2 mg/g. The adsorption process follows pseudo-second-order because it has two active sites, Brønsted acid sites (–SiOH and –SO3H) and Lewis acid sites (Si4+). Phenol in base condition undergoes a deprotonation reaction that is stabilized by the acid-active sites of the SLM adsorbent through intermolecular forces. Considering the large adsorption capacity and quick kinetic, the SLM adsorbent can be a promising cheap and green material to remove phenolic substances in wastewater, especially in the river near the medical facility. Copyright © 2024 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Pyrolysis-derived activated carbon from Colombian cashew (Anacardium occidentale) nut shell for valorization in phenol adsorption

Pyrolysis-derived activated carbon from Colombian cashew (Anacardium occidentale) nut shell for valorization in phenol adsorption

Large-scale preparation of Na2CO3-modified attapulgite adsorbents for efficient removal of p-Nitrophenol in wastewater

Developing adsorbents with ultrahigh adsorption capacity for phenol-containing wastewater is crucial to solving the problem of water pollution. However, the adsorbents currently used still have the disadvantages of low adsorption capacity, slow adsorption kinetics and difficulty in large-scale preparation. Herein, a facile and environmentally friendly inorganic salt (Na2CO3)-assisted modification method is employed to produce a large-scale attapulgite (ATP)-based adsorbents with high adsorption efficiency for p-nitrophenol (PNP) in wastewater, and its adsorption performance and mechanism are investigated in detail. The results shown that Na2CO3-modified ATP (S-ATP-1.0) possesses excellent adsorption performance with the maximum adsorption capacity of 1467.52 mg g−1 for PNP, which is significantly better than most previously reported adsorbents with similar functions. More excitingly, S-ATP-1.0 can maintains remarkable recyclability and structural stability even after 5 cycles. Structural characterization and theoretical calculations reveal that the excellent adsorption performance of S-ATP-1.0 for PNP is mainly attributed to the strong interaction between PNP and Na+ on the ATP surface. This work provides a new strategy for the large-scale preparation of phenolic adsorbents with low-cost and ultra-high adsorption properties, which is expected to be practically applied in the removal of highly concentrated PNP wastewater and environmental remediation.

Nitric acid modified powdered activated carbon for simultaneous adsorption of lead and phenol in aqueous solution

Powdered activated carbon (PAC) was modified with various concentrations of nitric acid (HNO3) to adsorb lead and phenol. The modification was carried out with HNO3 concentrations of 1 M (PAC-1), 3 M (PAC-3), and 5 M (PAC-5), respectively, and sodium hydroxide treatment was performed for neutralization. Oxygen functional groups such as phenolic hydroxyl, carboxy and lactone were produced after the HNO3 modification, and the surface area was decreased compared to unmodified PAC (PAC-W). A negative charge appeared in modified PACs due to the increased carboxyl groups, and PAC-5 exhibited the highest negative value as −34.56 mV. Batch adsorption was performed on both lead and phenol. Lead adsorption increased from 17.83 mg/g (PAC-W) to 28.70 mg/g (PAC-5) as HNO3 concentration increased. More lead was adsorbed in PAC-5 because of enhanced electrostatic attractions with increased oxygen functional groups. Conversely, phenol exhibited lower adsorption in PAC-5 (102.79 mg/g) than PAC-W (111.67 mg/g). Phenol adsorbed to PAC through π-π interactions, but reduced surface area and hydrophilic surface functional groups in modified PACs limited the adsorption of hydrophobic phenol molecules. In simultaneous adsorption, the lead and phenol concentration were fixed as 30 mg/L and 20 mg/L. The modified PACs exhibited a similar trend to single adsorption. However, the simultaneous lead and phenol adsorption on PAC-5 decreased to 26.74 mg/g and 84.13 mg/g, respectively. Lead ion reacted to oxygen functional groups while phenol occupied a less active site in PAC-5. The PAC-5 can be suitable for application in environmental decontamination due to the abundant functional groups.

Change of morphology of rice derived spherical hydrochar during activation

In many industrial scenarios, not only pore characteristics but also shape or macro morphology of activated carbon (AC) matters. Herein, influence of typical activating reagents (ZnCl2, H3PO4 or K2C2O4) on transformation of spherical hydrochar derived from rice were investigated. Activation of the hydrochar with H3PO4 and ZnCl2 at 550 °C promoted condensation reactions to yield more AC than that in activation with K2C2O4 at 800 °C (70.4 % with ZnCl2 versus 46.7 % with K2C2O4). The specific surface area (SBET) of AC produced with ZnCl2 or K2C2O4 showed similar values (1159.5 versus 1180.3 m2g−1). Nevertheless, the intensive cracking with K2C2O4 formed AC of more mesopores and micropores of larger diameter, facilitating adsorption of phenol (removal rate: 97.6 % versus 85.0 % over AC from ZnCl2). In-situ DRIFTS characterization of the activation indicated that H3PO4 and ZnCl2 catalyzed fast transformation of -OH and CO at < 300 °C via dehydration and condensation but still retained a large portion of H and O in AC. K2C2O4 catalyzed cracking but also retained oxygen-containing species and hindered aromatization. Pyrolysis of the hydrochar at 800 °C released around half of organic matters but did not result in burst of spheres. H3PO4 activated outer surface of hydrochar spheres, forming layered lamella structures via interparticle cross-condensation. ZnCl2 permeated into inner core of spheres and induced condensation inside, showing little effect on spherical morphology. Severe cracking with K2C2O4 led to partial crack of spheric structures and formation of piled particulate matters. Life cycle assessment (LCA) showed that the activation of the hydrochar with ZnCl2 showed the greatest impact on environment.

Citrus microcarpa biochar: A green solution for the adsorption of dyes and phenols

The most critical environmental issue of the twenty-first century is water scarcity. The diffusion of effluents into streams and ecosystems persists as a serious threat to public health and the stability of the food chain. The purpose of this research is to develop an adsorbent from an agricultural product that is efficient, environmentally friendly, and practical from an economical point of view. Spectroscopic techniques Such as UV–visible spectroscopy, Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, and Energy Dispersive X-ray analysis have been used to characterize the simple adsorbent as well as adsorbents integrated with dyes and phenolic compounds. The adsorption capability of biochar was evaluated for the removal of two dyes (Methyl violet and Malachite green) and 4-nitrophenol from wastewater. Various parameters, including dosage, time, concentration, pH, and temperature have been examined. The results revealed that the optimum dosage of methyl violet, malachite green, and 4-Nitrophenol is 0.05 g, 0.11 g, and 0.05 g respectively. The Optimum time duration for the removal of dyes and 4-nitrophenol is 30 min. The pseudo-2nd-order kinetic model demonstrates excellent compatibility with experimental results. The reaction between the adsorbent and methyl violet is endothermic, the reaction between malachite green and the adsorbent is exothermic, while the reaction between adsorbent and 4-Nitrophenol is endothermic. Among the Linear isotherms, Langmuir isotherm is best fitted for the removal of dyes and 4-Nitrophenol. Biochar prepared from Citrus microcarpa leaves exhibits efficient removal of Methyl Violet, Malachite Green, and 4-nitrophenol from wastewater.

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

AbstractElectrocatalytic 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.

Outside-in enhancement of phosphate solubilizing bacteria by sludge biochar for phenol remediation in soil: Pollution stress reduction, electron transfer gain and secretion regulation

The high toxicity of phenol poses a significant barrier to bacterial bio-removal capacity. This study innovatively proposes the utilization of sludge biochar (SB) to embed phosphate-solubilizing bacteria (CZB1), creating a composite system (SB-CZB1) that enhances the bio-removal efficiency of phenol. The research findings indicate that after being embedded with biochar, CZB1 achieved a significant enhancement (49.7 %–67.0 %) in phenol removal efficiency across different concentration gradients (1500, 2000, 2500 mg/L). SB component in the SB-CZB1 composite system provides a stable and favorable growth environment for CZB1, significantly enhancing microbial metabolic activity. Notably, it stimulates CZB1 to secrete succinic acid and malic acid (with increases of 3.8 % and 23.9 %, respectively), effectively mitigating the detrimental effects of phenol toxicity on microorganisms. Three-dimensional fluorescence and electrochemical analysis demonstrate that SB not only exhibits exceptional electrochemical performance but also stimulates CZB1 to generate redox-active substances (quinone components in humic acid). The electron transfer rates between microorganisms and phenol in the SB-CZB1 system are 10.75–22.71 times and 24.94–64.95 times higher than those in SB and CZB1 alone, respectively. Meanwhile, the abundant oxygen-containing functional groups (COH/COC, COOH, CO) on the surface of SB-CZB1 play a pivotal role in the adsorption and removal of phenol. Furthermore, pot experiments further reveal that the SB-CZB1 composite system significantly enhances the removal efficiency of phenol in soil (98.1 %). Additionally, the application of SB-CZB1 effectively modulated soil properties, notably increasing available potassium and available phosphorus content by 40.86 % and 136.69 %. This application not only enriched soil microbial diversity but also promoted the proliferation of native organic pollutant remediation bacteria in the soil. Notably, the proliferation of Bacillus species affiliated with CZB1 was the most significant, increasing by 82.1 %. This result confirms that biochar embedding technology effectively enhanced the colonization of CZB1 in the soil, thereby significantly accelerating the bio-removal process of phenol.

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 Chinese liquor 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, introducing oxygen-containing functional groups on the surface of DGC, thereby promoting the adsorption of Ru3+ and phenol. Additionally, the large specific surface area facilitated the dispersion of the active metal. 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.

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.