Caffeine removal using Elaeis guineensis activated carbon: adsorption and RSM studies

Efficient Decaffeination with Recyclable Magnetic Microporous Carbon from Renewable Sources: Kinetics and Isotherm Analysis

Rapid global urbanization and population growth have ignited an alarming surge in emerging contaminants in water bodies, posing health risks, even at trace concentrations. To address this challenge, novel water treatment and reuse technologies are required as current treatment systems are associated with high costs and energy requirements. These drawbacks provide additional incentives for the application of cost-effective and sustainable biomass-derived activated carbon, which possesses high surface area and low toxicity. Herein, we synthesized microporous activated carbon (MAC) and its magnetic derivative (m-MAC) from tannic acid to decaffeinate contaminated aqueous solutions. Detailed characterization using SEM, BET, and PXRD revealed a very high surface area (>1800 m2/g) and a highly porous, amorphous, heterogeneous sponge-like structure. Physicochemical and thermal analyses using XPS, TGA, and EDS confirmed thermal stability, unique surface moieties, and homogeneous elemental distribution. High absorption performance (>96 %) and adsorption capacity (287 and 394 mg/g) were recorded for m-MAC and MAC, respectively. Mechanistic studies showed that the sorption of caffeine is in tandem with multilayer and chemisorptive mechanisms, considering the models' correlation and error coefficients. π-π stacking and hydrogen bonding were among the interactions that could facilitate MAC-Caffeine and m-MAC-Caffeine bonding interactions. Regeneration and reusability experiments revealed adsorption efficiency ranging from 90.5-98.4 % for MAC and 88.6-93.7 % for m-MAC for five cycles. Our findings suggest that MAC and its magnetic derivative are effective for caffeine removal, and potentially other organic contaminants with the possibility of developing commercially viable and cost-effective water polishing tools.

In Vitro Evaluation of the Adsorption Efficacy of Biochar Materials on Aflatoxin B1, Ochratoxin A, and Zearalenone

Mycotoxin sequestration materials are important tools to reduce mycotoxin illness and enable proper handling of mycotoxin-contaminated commodities. Three food-grade bentonite clays and four generally recognized as safe (GRAS) charcoal/biochar carbon materials that are marketed as feed additives and supplements were evaluated for their ability to sequester the mycotoxins aflatoxin B1, ochratoxin A, and zearalenone. The surface area of the clays varied between 32.1 to 51.4 mg2/g, and the surface area of the carbon-based materials varied from 1.7 to 1735 mg2/g. In vitro, gastric fluid studies indicated that certain pine biochar and activated coconut charcoal could sequester high amounts (85+%) of the mycotoxins at 1 ppm levels or below. However, some biochar materials with lower surface area properties lacked binding capacity. The coconut shell charcoal and pine biochar utilize agricultural waste products in a manner that significantly reduces carbon emissions and provides valuable materials to minimize exposure to toxins found in food and feed.

Handleable TiO2-coated zeolitic material for photodecomposition of caffeine boosted by urine matrix

The photocatalytic decomposition of caffeine under UV-light irradiation was observed for the first time in a matrix of synthetic urine using granules of hydrogenated and iron-exchanged natural zeolite, coated with two loadings of TiO₂. A natural clinoptilolite-mordenite blend was used to prepare photocatalytic adsorbents coated with TiO₂ nanoparticles. The performance of the obtained materials was tested in the photodegradation of caffeine, a water contaminant of emerging concern. The photocatalytic activity was better in the urine matrix, due to the formation of surface complexes on the TiO₂ coating, cation exchange performed by the zeolite support, and use of the carrier electrons in the reduction of ions, affecting recombination of the electrons and holes during photocatalysis. The composite granules maintained photocatalytic activity for at least four cycles, with more than 50% of caffeine removal in the synthetic urine matrix.

Adsorption of caffeine using steel wastes

Caffeine is the most widespread active pharmaceutical compound in the world, generally studied as a tracer of human pollution, since caffeine levels in surface water correlate with the anthropogenic load of domestic wastewater. This work investigated the use of different steel wastes named as SW-I, SW-II, SW-II, SW-IV, SW-V, and SW-VI in the adsorption of caffeine. These materials were pretreated and characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and point of zero charge. The samples are mainly composed of iron (hematite and magnetite). The caffeine adsorption test indicated that SW-VI (steel slag dust) is the most efficient and promising (removal around 51.68%) in relation to the other residues, which it was selected for further studies. Equilibrium time was reached within 96 h of contact between the adsorbent and the adsorbate, with removal of 84.00%, 81.09%, and 73.19% for the initial concentrations of 10 mg L^-1, 20 mg L^-1, and 30 mg L^-1 of caffeine. The pseudo-first-order, pseudo-second-order, and Elovich models presented a good fit to the experimental data. However, the pseudo-first order model described better the experimental behavior. Adsorption isotherms were performed at three temperatures (298, 308, and 318 K). The maximum adsorption capacity was 17.46 ± 2.27 mg g^-1, and experimental data were better fitted by the Sips isotherm. Values of ΔG° and parameters equilibrium of the models of Langmuir, Sips, and Temkin were calculated from the standard enthalpies and standard entropies estimated. The values of ΔG° were negative for the temperatures studied indicating that the adsorption process is viable and spontaneous. Negative values for ΔH° were also found, indicating that the process of caffeine adsorption by SW-VI is an exothermic process (0 to -40 kJ mol^-1). Thus, the adsorption of caffeine by SW-VI is a physical process. The SW-VI material showed economic viability and promising for the adsorption of caffeine in aqueous media.

Mechanism and behavior of caffeine sorption: affecting factors

Caffeine is one of the emerging pollutants with a diverse chemical composition. It is mixed with the hydrobiota as a result of its high consumption, and when certain dose intervals are exceeded, it re-enters the human body through indirect routes such as plants, animals, soil, water, and the food chain, causing health problems that are difficult or impossible to treat, and irreversible environmental problems. This situation raises concerns about the presence of pollutants emerging in water resources, igniting interest in water treatment processes and the development of alternative methods. Although there are several methods for removing caffeine from aqueous media, adsorption is the most popular because it is less expensive than other methods and has the highest removal efficiency. Furthermore, it has the benefit of selectively attaching the molecules in solution. In this article, studies on the caffeine adsorption process have been examined, and the caffeine adsorption efficiency of various adsorbents has been summarized by compiling information such as pH, contact time, temperature, and concentration of adsorbent and adsorbate, which are considered as optimum processing conditions. The binding mechanism was investigated, and it was clearly stated how caffeine adheres to the adsorbent surface. Among the equilibrium adsorption isotherms, the isotherm model with the best agreement with the experimental data was attempted to be determined. Many studies clearly show that the process of developing environmentally friendly and high-capacity adsorbents in sustainable processes and in harmony with the circular economy is increasing day by day.

Highly effective adsorption of caffeine by a novel activated carbon prepared from coconut leaf

The disposal of coconut wastes is costly and damaging to the environment, but its uses are advantageous activated carbons production. Coconut leaves waste were used for activated carbon production by pyrolysis at 500° C and activation with potassium carbonate. The activated carbon was used for caffeine removal from aqueous solution. The coconut leaves activated carbon showed a predominantly amorphous structure from X-ray diffraction analysis and a pH at the zero charge point of 7.9. From the N₂ adsorption/desorption method, the adsorbent showed a predominance of mesopores, with average pore size of 45.48 ηm and a surface area of 678.03 m²/g. From kinetic studies the data followed the pseudo-second order, where the intraparticle diffusion can be neglected. The adsorption isotherms were satisfactorily adjusted for the Redlich-Peterson model and a type curve L was identified. The thermodynamic parameters showed that adsorption occurred spontaneously, was exothermic and governed by physical adsorption. The artificial neural networks developed were capable of predicting both kinetics and equilibrium adsorption data under different operating conditions and was comparable to the traditional models available in literature in the training experiments, encouraging its use for data generalization when an efficient dataset is used. In conclusion, coconut leaves waste showed to be a promising feedstock to produce activated carbon aiming caffeine removal from water and wastewater.

Growth of MWCNTs from Azadirachta indica oil for optimization of chromium(VI) removal efficiency using machine learning approach

The main objective of the present study is to develop artificial neural networks (ANN) to predict the adsorption efficiency of multi-walled carbon nanotubes (MWCNTs) on Cr(VI) removal. Polydisperse MWCNTs were synthesized at 750 °C on alumina supported Fe-Co-Mo catalyst using CVD (chemical vapor deposition)-assisted spray pyrolysis of Azadirachta indica (Neem) oil under inert Argon (Ar) atmosphere. Growth of MCWNTs with inner diameters between 9 and 14 nm was corroborated by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction analysis (XRD), and Raman spectral evidence assessments. The metal-ion adsorbent capacity (Cr-VI) of the as such prepared MWCNTs was examined for industrial purposes. Different parameters such as adsorption isotherms, kinetics, and thermodynamic parameters were analyzed for the removal of metal ions with MWCNTs. The results of isotherm, kinetic, and thermodynamic study indicated that the process suited well with Langmuir isotherm, pseudo second-order kinetics, and followed endothermic reaction, respectively. The effects of parameters such as adsorbent dosage, concentration of chromium ion (Cr-VI), pH, and contact time were studied to optimize the maximum removal of Cr(VI). In order to optimize the process conditions using Artificial Neural Networks, Box-Behnken design (BBD) was used to design the batch adsorption experiments, and the resulting datasets were used as the input for ANN. To predict the adsorption efficiency, various ANN architectures were examined using different training algorithms, number of neurons in the hidden layer, and the transfer function for the hidden and output layers. A neural network structure with Levenberg-Marquardt (LM) training algorithm, 14 hidden neurons, and tangent sigmoid transfer function at the hidden layer and logarithmic sigmoid transfer function at the output layer furnished the best level of prediction results. Comparing with experimental data, the optimal model capitulated mean square error (MSE),and correlation coefficient (R²) of 0.0324 and 0.99512, respectively. The results showed that ANN is well-organized in predicting the adsorption efficiency of MWCNTs for Cr(VI) metal ion removal process.

Removal of Emerging Contaminants as Diclofenac and Caffeine Using Activated Carbon Obtained from Argan Fruit Shells

Activated carbons from argan nutshells were prepared by chemical activation using phosphoric acid H3PO4. This material was characterized by thermogravimetric analysis, infrared spectrometry, and the Brunauer–Emmett–Teller method. The adsorption of two emerging compounds, a stimulant caffeine and an anti-inflammatory drug diclofenac, from distilled water through batch and dynamic tests was investigated. Batch mode experiments were conducted to assess the capacity of adsorption of caffeine and diclofenac from an aqueous solution using the carbon above. Adsorption tests showed that the equilibrium time is 60 and 90 min for diclofenac and caffeine, respectively. The adsorption of diclofenac and caffeine on activated carbon from argan nutshells is described by a pseudo-second-order kinetic model. The highest adsorption capacity determined by the mathematical model of Langmuir is about 126 mg/g for diclofenac and 210 mg/g for caffeine. The thermodynamic parameters attached to the studied absorbent/adsorbate system indicate that the adsorption process is spontaneous and exothermic for diclofenac and endothermic for caffeine.

Optimization of ketoprofen adsorption from aqueous solutions and simulated effluents using H2SO4 activated Campomanesia guazumifolia bark

This study used the bark of the forest species Campomanesia guazumifolia modified with H₂SO₄ to absorb the anti-inflammatory ketoprofen from aqueous solutions. FTIR spectra confirmed that the main bands remained after the chemical treatment, with the appearance of two new bands related to the elongation of the carbonyl group present in hemicellulose. Micrographs confirmed that the surface started to contain a new textural shape after acid activation, having new pores and cavities. The drug adsorption's optimum conditions were obtained by response surface methodology (RSM). The adsorption was favored at acidic pH (2). The dosage of 1 g L^-1 was considered ideal, obtaining good indications of removal and capacity. The Elovich model very well represented the kinetic curves. The isotherm studies indicated that the increase in temperature negatively affected the adsorption of ketoprofen. A maximum adsorption capacity of 158.3 mg g^-1 was obtained at the lower temperature of 298 K. Langmuir was the best-fit isotherm. Thermodynamic parameters confirmed the exothermic nature of the system (ΔH⁰ = -8.78 kJ mol^-1). In treating a simulated effluent containing different drugs and salts, the removal values were 35, 50, and 80% at 15, 30, and 180 min, respectively. Therefore, the development of adsorbent from the bark of Campomanesia guazumifolia treated with H₂SO₄ represents a remarkable alternative for use in effluent treatment containing ketoprofen.

A Review of Caffeine Adsorption Studies onto Various Types of Adsorbents

A systematic literature review of publications from 2000 to 2020 was carried out to identify research trends on adsorbent materials for the removal of caffeine from aqueous solutions. Publications were retrieved from three databases (Scopus, Web of Science, and Google Scholar). Words "adsorption AND caffeine" were examined into titles, abstracts, and keywords. A brief bibliometric analysis was performed with emphasis on the type of publication and of most cited articles. Materials for the removal of caffeine were classified according to the type of material into three main groups: organic, inorganic, and composites, each of them subdivided into different subgroups consistent with their origin or production. Tables resume for each subgroup of adsorbents the key information: specific surface area, dose, pH, maximum adsorption capacity, and isotherm models for the removal of caffeine. The highest adsorption capacities were achieved by organic adsorbents, specifically those with granular activated carbon (1961.3 mg/g) and grape stalk activated carbon (916.7 mg/g). Phenyl-phosphate-based porous organic polymer (301 mg/g), natural sandy loam sediment (221.2 mg/g), composites of MCM-48 encapsulated graphene oxide (153.8 mg/g), and organically modified clay (143.7 mg/g) showed adsorption capacities lower than those of activated carbons. In some activated carbons, a relation between the specific surface area (SSA) and the maximum adsorption capacity (Q max) was found.

Miscanthus as a carbon precursor for graphene oxide: A possibility influenced by pyrolysis temperature

This study investigates the potential of producing graphene oxide (GO) from biomass via green (comparatively) processing and the impact of graphitization temperature on GO quality. Our findings show that it is possible to convert biomass into highly pyrolytic biochar, followed by shear exfoliation to produce few-layer GO. However, pyrolysis temperature is key in ensuring that the biochar is suited for effective exfoliation. Low temperatures (<1000 °C) would preserve undesirable heterogenous, complex cellular structure of biomass whilst excessive temperatures (≥1300 °C) result in uncontrolled melting, coalescence and loss of functional groups. Results show 1200 °C to be the optimum graphitization temperature for miscanthus, where the resultant biochar is highly aromatic with sufficient functional groups to weaken van der Waals forces, thus facilitating exfoliation to form 6-layer GO with specific surface area of 545.3 m²g^-1. This study demonstrates the potential of producing high quality, fit-for-purpose graphene materials from renewable sources.

Caffeine removal from aqueous media by adsorption: An overview of adsorbents evolution and the kinetic, equilibrium and thermodynamic studies

Caffeine is an emerging pollutant and is considered the most representative pollutant of the Pharmaceutical Active due to its high consumption by the general population. It can be used to track pollution caused by humans. Different technologies have been employed to remove the caffeine from aqueous media, however the adsorption has been preferred due to its simplicity, high removal efficiency, operational and implementation facility and low cost. This paper provides a systematic review of the published peer-reviewed literature concerned with caffeine removal by the adsorption process. The Scopus and ScienceDirect databases were used to identify relevant articles researches on caffeine removal. Many authors have studied caffeine's adsorption equilibrium in aqueous media, different conditions, and different adsorbents. This paper aims to uncover the overall trend of adsorbent used, kinetic and thermodynamic studies. The impact of pH, temperature, adsorbent dosage and competitive effect were presented and analyzed. It was observed that the adsorption capacities ranged between 10 and 1000 mg g^-1, according to the nature and properties of the adsorbent. The pseudo-second order (kinetic model) and the Langmuir isotherm model showed the best adjustment of the experimental data from caffeine adsorption in most studies. The mechanistic understanding of adsorption and the development of new adsorbents are still a matter of future research, as well as the use of other kinetic models based on statistical factors and the thermodynamic studies should be considered.

Kinetics of nutrients remediation from sugar industry effluent-treated substrate using Agaricus bisporus: mushroom yield and biochemical potentials

This study investigated the yield and biochemical potential of Agaricus bisporus mushroom cultivated on agricultural waste substrate supplemented with treated sugar industry effluent (SIE). Laboratory-scale experiments were performed for the cultivation of A. bisporus on a mixture of wheat straw and sugar cane bagasse moistened with different doses of borewell water (BWW) and treated SIE (0-100%). Besides this, the simultaneous effects of the SIE amendment on total Kjeldahl's nitrogen (TKN) and total phosphorus (TP) contents of substrate and kinetics of their utilization by A. bisporus were studied. Results showed a relatively higher utilization of TKN (38.10 ± 1.60%) and TP (47.4 ± 6.44%) in a 25:75 ratio of BWW and SIE, respectively. The kinetics studies of TKN and TP utilization using Lineweaver-Burk models described the maximum specific utilization rates (V _max) of 0.165 and 0.125 mg·kg^-1·d^-1 and saturation points (K _m ) of 72.401 and 33.283 mg·kg^-1, respectively, which are in good agreement as indicated by R ² values (> 0.90). In addition, the maximum significant (P < 0.01) yield (159.31 ± 8.85 g·Kg^-1), biological efficiency (106.21 ± 3.84%), total phenols (3.03 ± 0.07 mg·g^-1), ascorbic acid (0.44 ± 0.03 mg·g^-1), and β-carotene (3.36 ± 0.05 μg·g^-1) of A. bisporus were observed using the same treatment. Therefore, this paper reported sustainable utilization of TKN and TP nutrients from SIE for A. bisporus mushroom cultivation.

Successful adsorption of bright blue and methylene blue on modified pods of Caesalpinia echinata in discontinuous system

Pods of the forest species Caesalpinia echinata were used as an alternative adsorbent to remove bright blue (BB) and methylene blue (MB) dyes. The raw and acid-treated samples were characterized by techniques like SEM, XRD, and FTIR. The acid-treated pod sample was characterized by an amorphous structure containing several cavities, bumps, and functional groups. The Elovich model was the most satisfactory to describe the adsorption kinetic data. The isothermal studies were better described by the Langmuir model for BB dye, with a maximum capacity of 261 mg g^-1, and Tóth model for MB dye, giving a maximum capacity of 288 mg g^-1. The thermodynamic study indicated a spontaneous and favorable process and endothermic nature for both dyes. In the treatment of two simulated effluents containing a mixture of different compounds such as dyes and salts, to simulate real wastewaters, the adsorbent was highly efficient, presenting around 80% of color removal for both effluents. Therefore, the acid-treated pods of Caesalpinia echinata have great potential to be applied as an alternative adsorbents in treating colored effluents in discontinuous systems.