Fixed-Bed Adsorption of Ciprofloxacin onto Bentonite Clay: Characterization, Mathematical Modeling, and DFT-Based Calculations

A robust self-regenerating graphene-based adsorbent for pharmaceutical removal in various water environments

The presence of active pharmaceutical ingredients (APIs) in wastewater effluents and natural aquatic systems threatens ecological and human health. While activated carbon-based adsorbents, such as GAC and PAC, are widely used for API removal, they exhibit certain deficiencies, including reduced performance due to the presence of natural organic macromolecules (NOMs) and high regeneration costs. There is growing demand for a robust, stable, and self-regenerative adsorbent designed for API removal in various environments. In this study, we synthesized a self-generating metal oxide nano-composite (S-MGC) containing titanium dioxide (TiO2) and silicon dioxide (SiO2) combined with 3D graphene oxide (GO) to adsorb APIs and undergo regeneration via light illumination. We determined optimal TiO2:SiO2:GO compositions for the S-MGCs through experiments using a model contaminant, methylene blue. The physical and chemical properties of S-MGCs were characterized, and their adsorption and photodegradation capabilities were studied using five model APIs, including sulfamethoxazole, carbamazepine, ketoprofen, valsartan, and diclofenac, both in single-component and multi-component mixtures. In the absence of TiO2/SiO2, 3D graphene oxide (CGB) displayed better adsorption performance compared to GAC, and S-MGCs further improve CGB's adsorption capacity. This performance remained consistent in two complex water environments: aqueous solutions at varying NOM levels and artificial urine. TiO2 supported on the GO surface exhibits similar photocatalytic activity to suspended TiO2. In a continuous fixed-bed column test, S-MGCs demonstrated robust API adsorption performance that is maintained in the presence of NOM or urine, and can be regenerated through multiple cycles of adsorption and light illumination.

Valorization of sponge iron industrial waste into iron-modified zeolite X for ciprofloxacin removal: a multi-parameter optimization study

Ciprofloxacin (CIP), a commonly used antibiotic, is frequently detected in water bodies and the natural environment. The profound health consequences of CIP have led to growing attention focusing on environmental concerns. Adsorption is highly preferred because of its adaptability and remarkable efficiency in removing CIP. Therefore, the current work focuses on synthesizing an eco-friendly and economical adsorbent for removing CIP. The work aims to remove CIP using zeolite X (ZX), synthesized from dolochar, and subsequently modified ZX into iron-modified zeolite X (FeZX) via ion exchange. The synthesized FeZX had a crystallinity of 82.701%, an average pore size of 5.917 nm, a micropore volume of 0.298 cc/g, a micropore area of 451.807 m2/g, and a total surface area of 478.521 m2/g. The effect of parameters such as initial CIP concentration, pH, contact period, adsorbent dosage, and iron dosage was analyzed in the batch adsorption studies of CIP using ZX and FeZX. CIP removal of 37.786% was achieved using ZX; hence, the adsorption parameters were optimized to maximize the CIP removal using response surface methodology (RSM), specifically Box-Behnken Design (BBD) using FeZX. Maximum removal of 97.974% was achieved under optimum conditions of 8.06 pH, contact period of 59.422 min, CIP concentration of 17.117 mg/L, and adsorbent dosage of 0.478 g/L. Freundlich isotherm and pseudo-second-order kinetic models were the most accurate representations of the experimental data. The findings indicate the significance of using this iron-modified mesoporous zeolite as an adsorbent for efficiently treating CIP wastewater.

Machine learning for the adsorptive removal of ciprofloxacin using sugarcane bagasse as a low-cost biosorbent: comparison of analytic, mechanistic, and neural network modeling

Contamination with traces of pharmaceutical compounds, such as ciprofloxacin, has prompted interest in their removal via low-cost, efficient biomass-based adsorption. In this study, classical models, a mechanistic model, and a neural network model were evaluated for predicting ciprofloxacin breakthrough curves in both laboratory- and pilot scales. For the laboratory-scale (d = 2.2 cm, Co = 5 mg/L, Q = 7 mL/min, T = 18 °C) and pilot-scale (D = 4.4 cm, Co = 5 mg/L, Q = 28 mL/min, T = 18 °C) setups, the experimental adsorption capacities were 2.19 and 2.53 mg/g, respectively. The mechanistic model reproduced the breakthrough data with high accuracy on both scales (R2 > 0.4 and X2 < 0.15), and its fit was higher than conventional analytical models, namely the Clark, Modified Dose-Response, and Bohart-Adams models. The neural network model showed the highest level of agreement between predicted and experimental data with values of R2 = 0.993, X2 = 0.0032 (pilot-scale) and R2 = 0.986, X2 = 0.0022 (laboratory-scale). This study demonstrates that machine learning algorithms exhibit great potential for predicting the liquid adsorption of emerging pollutants in fixed bed.

Tetracycline decontamination from aqueous media using nanocomposite adsorbent based on starch-containing magnetic montmorillonite modified by ZIF-67

In the present study, starch/zeolitic imidazole framework-67 (ZIF-67) modified magnetic montmorillonite nanocomposite adsorbent to remove tetracycline (TC) as an emerging antibiotic-based contaminant from aqueous media. The surface properties of the adsorbents were investigated using FTIR, XRD, SEM, EDX-Map, XPS, TEM, BET, and VSM analysis. The specific surface area of MMT, St/MMT-MnFe2O4, and St/MMT-MnFe2O4-ZIF-67 magnetic nanocomposite samples were found to be 15.63, 20.54, and 588.41 m2/g, respectively. The influence of pH, adsorbent amount, initial TC concentration, temperature, contact time, and coexisting ions on TC elimination was explored in a batch adsorption system. The kinetic and equilibrium data were well matched with the pseudo-second-order and Langmuir isotherm models, respectively. The maximum monolayer adsorption capacities of TC were obtained to be 40.24, 66.1, and 135.2 mg/g by MMT, St/MMT-MnFe2O4, and St/MMT-MnFe2O4-ZIF-67 magnetic nanocomposite adsorbents, respectively. Also, thermodynamic studies illustrated that the TC adsorption process is exothermic and spontaneous. Furthermore, the magnetic nanocomposite adsorbent St/MMT-MnFe2O4-ZIF-67 showed good reusability and could be recycled for up to five cycles. This excellent adsorption performance, coupled with the facile separation of the magnetic nanocomposite, gave St/MMT-MnFe2O4-ZIF-67 a high potential for TC removal from aqueous media.

Quantitative Evaluation of the Effects of Salt Concentration and pH on the Self-Assembly of Kaolin Nanoplatelets

Diffusion of pollutants in the earth's strata threatens both the environment and human health. The clay soil microstructure that plays a crucial role in the diffusion of pollutants is significantly influenced by the pore water chemistry. However, there is still a lack of quantitative evaluation of pore water chemistry on clay fabric evolution. To bring new insights, we systematically examined the impact of water chemistry (mainly refers to salt ion concentration and pH) on the self-assembly form (fabric) of kaolin platelets and evaluated the fabric quantitatively. The results show that as the salt ion concentration increases, the "kaolin book" structure is formed, which can be captured by the (001) and (020) pole figures. Under acidic conditions, kaolin platelets turn randomly arranged; however, with the increase of pH, the edge-to-face (EF) microstructure of kaolin platelets gradually changes to a face-to-face (FF) structure. Under alkali-eq conditions, kaolin platelets form a dispersion assembly dominated by FF repulsion. However, the strong alkaline condition triggers the decomposition of kaolin, leading to a notable decrease in the maximum pole density. The conclusions were substantiated through insightful AFM tests. Moreover, we addressed the advantages and limitations of 1DXRD and 2DXRD by analyzing the trend between the OI and pole density, with 2DXRD being favored for its accuracy. Overall, this study provides insights into clay platelets and the self-assembly of kaolin under different water chemistry conditions, which have significant implications for predicting and modeling the physical properties of clay under special environmental conditions.

Design and Development of a Pilot-Scale Industrial Wastewater Treatment System with Plant Biomass and EDTA

The impact generated by the indiscriminate disposal of heavy metals into the different bodies of water is not only environmental but also social due to the health effects it produces in several organisms, including ourselves. Therefore, treatment systems around the world are the subject of continuous research to find treatment systems that are economical, efficient, and easy to implement in the industries that generate these increasingly harmful impacts on society and the environment in general. One way to design and develop systems of water treatment is that which takes advantage of the waste generated, such as the waste from the E. crassipes plant. The conditions of this plant make it perfect due to its abundant biomass and important content of cellulose and hemicellulose. Nevertheless, in almost all the investigations that characterize the way in which the biomass of this plant adsorbs heavy metals, it does so under laboratory conditions, being very far from the reality of industrial discharges. The objective of this project is to design and develop a pilot-scale industrial wastewater treatment system with plant biomass and EDTA. Three pilot-scale systems were built with EDTA-modified biomass in different concentrations, giving the parameters of the design for the development of a system that can treat around 80 L of Chromium (VI) contaminated water. This treatment system with E. crassipes biomass and EDTA with proportions of 9:1 costs around USD 10, which is quite cheap compared to conventional ones.

Green synthesis, characterization, and application of Fe3O4 nanoparticles for methylene blue removal: RSM optimization, kinetic, isothermal studies, and molecular simulation

Methylene Blue (MB) is a cationic dye causing various health problems such as asthma, heartbeat, eye and skin irritation, nausea, and distress during prolonged exposure. In this regard, the green magnetite nanoparticle was synthesized using the extract of Prosopis farcta. The synthesized Fe₃O₄nanoparticle was characterized by X-ray powder diffraction (XRD), Field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), Fourier transforms Infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM), and Brunauer-Emmett-Teller (BET). The corresponding parameters, including the primary concentration of MB (5-65 mg/L), the dose of synthesized nanoparticle (0.025-0.925 g/L), solution pH (3-11), and contact time (20-60 min), were considered. Also, central composite design (CCD), as one of the response surface methodologies (RSM), was used for the related modelling and optimization. The particle size of the adsorbent was between 5 and 70 nm, and the nanoparticle has 206.75 m²/g of a specific surface, 6.1 nm of average pore size, and 0.3188 cm³/g of the total pore volume. The optimal conditions for MB removal by the nanoparticle were found to follow an initial MB concentration of 20 mg/L, 0.7 g/L of the nanoparticle dose, pH = 9, and a contact time of 50 min. The pseudo-second-order (PSO) and Freundlich models were the best kinetic and isothermal models for MB removal by the synthesized nanoparticle. Molecular modelling was used to optimize the MB molecular configuration and compute HOMO-LUMO energies, quantum-chemical descriptors, and molecular electrostatic potential to evaluate the nature reactivity of the MB molecule.

Electrodegradation of cyclophosphamide in artificial urine by combined methods

The degradation of the chemotherapeutic drug cyclophosphamide in artificial urine was evaluated by Electrochemical Advanced Oxidation Processes (EAOP). The system consisted of an electrochemical flow reactor with a commercial DSA^® electrode (nominal composition Ti / Ru_0,3Ti_0,7O₂) and Ti-mesh cathode. In order to assess the best parameters, the effect of current density, time and flow rate were analyzed using an initial 2³ factorial design. The chosen response variable was the energy efficiency to produce free chlorine species (HClO/ClO^-). After obtaining the most significant factors, the Central Composite Design (CCD) was performed, where the optimum conditions were determined for the current density range (11.714 mA cm^-2 and 66.57 mA cm^-2), flow rate (31.33 mL min^-1) and time range (19 and 37 min). Under an optimized condition, the efficiency of other combined methods (photo-assisted electrochemical, photochemical, sonoelectrochemical and photo-assisted sonoelectrochemical) was evaluated. The efficiency of degradation processes was determined by removal of Chemical Oxygen Demand (COD), creatinine and urea. Analysis by HPLC demonstrates that the cyclophosphamide was substantially removed during the treatment process of ∼77%. Based on these results, it can be observed that the coupling between electrochemical and photochemical processes is a promising alternative for the treatment of this effluent, as a marked reduction of organic matter is observed (63, 94% of creatinine, 29.62% of urea, 39.1% of TOC) and a low treatment cost ratio.

Hybrid process of adsorption and electrochemically based green regeneration of bentonite clay for ofloxacin and ciprofloxacin removal

Removal of emerging contaminants, such as antibiotics, from wastewater by adsorption is a simple, low-cost, and high-performance process; however, regeneration and reuse of the exhausted adsorbent are necessary to make the process economically viable. This study aimed to investigate the possibility of electrochemical-based regeneration of clay-type materials. For this, the calcined Verde-lodo (CVL) clay was saturated with the antibiotics ofloxacin (OFL) and ciprofloxacin (CIP) in one-component systems by an adsorption process and then subjected to photo-assisted electrochemical oxidation (0.45 A, 0.05 mol/L NaCl, UV-254 nm, and 60 min), which promotes both pollutant degradation and adsorbent regeneration. The external surface of the CVL clay was investigated by X-ray photoelectron spectroscopy before and after the adsorption process. The influence of regeneration time was evaluated for the CVL clay/OFL and CVL clay/CIP systems, and the results demonstrate high regeneration efficiencies after 1 h of photo-assisted electrochemical oxidation. Clay stability during regeneration was investigated by four successive cycles in different aqueous matrices (ultrapure water, synthetic urine, and river water). The results indicated that the CVL clay is relatively stable under the photo-assisted electrochemical regeneration process. Furthermore, CVL clay was able to remove antibiotics even in the presence of natural interfering agents. The hybrid adsorption/oxidation process applied here demonstrated the electrochemical-based regeneration potential of CVL clay for the treatment of emerging contaminants, since it can be operated quickly (1h of treatment) and with lower consumption of energy (3.93 kWh kg^-1) than the traditional method of thermal regeneration (10 kWh kg^-1).

Decipher the molecular descriptors and mechanisms controlling sulfonamide adsorption onto mesoporous carbon: Density functional theory calculation and partial least-squares path modeling

Mesoporous carbons (MCs) exhibit excellent removal efficiencies to various organic chemicals. However, how the properties of chemicals influence the adsorption mechanisms and further determine their adsorption onto MCs are poorly understood. We investigated the adsorption of 22 sulfonamides (SAs) onto four MCs, and further uncovered the major molecular descriptors and adsorption mechanisms influencing the adsorption by density functional theory (DFT) and partial least-squares path modeling (PLS-PM). The results revealed that the excess molar refraction (E), McGowan's molar volume (V), energy of the highest occupied molecular orbital (E_HOMO), hardness (H), and most positive net charge on carbon atom (Q_c⁺) were identified as the indirect factors affecting the distribution coefficient (logK_D), by influencing the BE(π-π), BE(H), and logK_ow. BE(π-π) and logK_ow displayed significant direct impacts on logK_D (p < 0.05), while BE(H) showed insignificant direct influences on logK_D (p > 0.05). The PLS-PM results indicate the main driving forces for SAs adsorption including π-π interactions, hydrophobic effects, and hydrogen bonding. This study provides a new perspective on revealing the adsorption mechanisms, and the identified factors can be used to develop the quantitative model to further predict the adsorption of SAs onto MCs.

Unraveling the Origin of Enhanced Activity of the Nb2O5/H2O2 System in the Elimination of Ciprofloxacin: Insights into the Role of Reactive Oxygen Species in Interface Processes

The overlooked role of reactive oxygen species (ROS), formed and stabilized on the surface of Nb₂O₅ after H₂O₂ treatment, was investigated in the adsorption and degradation of ciprofloxacin (CIP), a model antibiotic. The contribution of ROS to the elimination of CIP was assessed by using different niobia-based materials in which ROS were formed in situ or ex situ. The formation of ROS was confirmed by electron paramagnetic resonance (EPR) and Raman spectroscopy. The modification of the niobia surface charge by ROS was monitored with zeta potential measurements. The kinetics of CIP removal was followed by UV-vis spectroscopy, while identification of CIP degradation products and evaluation of their cytotoxicity were obtained with liquid chromatography-mass spectrometry (LC-MS) and microbiological studies, respectively. Superoxo and peroxo species were found to significantly improve the efficiency of CIP adsorption on Nb₂O₅ by modifying its surface charge. At the same time, it was found that improved removal of CIP in the dark and in the presence of H₂O₂ was mainly determined by the adsorption process. The enhanced adsorption was confirmed by infrared spectroscopy (IR), total organic carbon measurements (TOC), and elemental analysis. Efficient chemical degradation of adsorbed CIP was observed upon exposure of the Nb₂O₅/H₂O₂ system to UV light. Therefore, niobia is a promising inorganic adsorbent that exhibits enhanced sorption capacity toward CIP in the presence of H₂O₂ under dark conditions and can be easily regenerated in an environmentally benign way by irradiation with UV light.

Adsorption of antibiotic cefazolin in organoclay fixed-bed column: characterization, mathematical modeling, and DFT-based calculations

Cefazolin (CFZ) is an antibiotic widely used in veterinary and human medicine that has been detected in high residual levels in the environment and is therefore considered an emerging contaminant. This work evaluated the adsorption of this contaminant by Spectrogel® type C organoclay, in continuous mode using a fixed-bed column. The fluid dynamics and the effect of the CFZ concentration were evaluated. In addition, prior and post-process organoclay were characterized. The continuous system under the conditions of C₀ = 0.3 mmol/L and Q = 0.1 mL/min presented lower values of mass transfer zone (5.88 cm), whereas the system with C₀ = 0.5 mmol/L and Q = 0.1 mL/min achieved higher CFZ adsorption capacity (20 µmol/g). Phenomenological and mass-transfer models were applied to the experimental data. The dual-site diffusion (DualSD) model better described the breakthrough (BTC) data. Furthermore, density functional theory (DFT) calculation was performed at the molecular level to provide a better comprehension of CFZ adsorption.

Ultrasensitive fluorescence detection of norfloxacin in aqueous medium employing a 2D Zn(ii)-based coordination polymer

A 2D fluorescent coordination polymer, {[Zn(L)0.5(mip)] 1.75H2O}n (1), was successfully assembled. 1 was developed as an ultrasensitive fluorescent probe for the sensing of norfloxacin (NOR) in water.