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In this work, iron-bearing mining reject was employed as an alternative and potential low-cost catalyst to degrade phenol in water by photo-Fenton strategy. Various techniques, including SEM-EDS, BET, FTIR, and XRD, were applied to evaluate the material's properties. Process parameters such as hydrogen peroxide concentration, catalyst dosage, and pH were studied to determine the optimum reaction conditions ([catalyst] = 0.75 g L-1, [H2O2] = 7.5 mM, and pH = 3). Phenol degradation and mineralization efficiencies at 180 and 300 min were 96.5 and 78%, respectively. These satisfactory results can be associated with the iron amount present in the waste sample. Furthermore, the material showed high catalytic activity and negligible iron leaching even after the fourth reuse cycle. The degradation behavior of phenol in water was well represented by a kinetic model based on the Fermi function. The iron-bearing mining reject can be considered a potential photo-Fenton catalyst for phenol degradation in wastewater.

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The objective of this study is to develop a low-cost biosorbent using residual seeds of the Citrullus lanatus fruit for the removal of cationic dyes. Physicochemical parameters such as pH, adsorbent mass, contact time, and temperature were evaluated for their effects on dye removal. The biosorbent is composed of lignin and cellulose, exhibiting a highly heterogeneous surface with randomly distributed cavities and bulges. The adsorption of both dyes was most effective at natural pH with a dosage of 0.8 g L-1. Equilibrium was reached within 120 min, regardless of concentration, indicating rapid kinetics. The Elovich model and pseudo-second-order kinetics were observed for crystal violet and basic fuchsin dye, respectively. The Langmuir model fitted well with the equilibrium data of both dyes. However, the increased temperature had a negative impact on dye adsorption. The biosorbent also demonstrated satisfactory performance (R = 43%) against a synthetic mixture of dyes and inorganic salts, with a small mass transfer zone. The adsorption capacities for crystal violet and basic fuchsin dye were 48.13 mg g-1 and 44.26 mg g-1, respectively. Thermodynamic studies confirmed an exothermic nature of adsorption. Overall, this low-cost biosorbent showed potential for the removal of dyes from aqueous solutions.

In this work, a novel biosorbent was developed using residual Citrullus lanatus fruit seeds that can efficiently remove cationic dyes from aqueous solutions. The biosorbent's composition includes lignin and cellulose, and its surface structure is highly heterogeneous, consisting of randomly distributed cavities and bulges. The biosorbent demonstrated a rapid and efficient adsorption capacity for both crystal violet and basic fuchsin, regardless of dye concentration. Moreover, the biosorbent was successfully employed in the treatment of a synthetic mixture containing several dyes and inorganic salts. Finally, the application of the biosorbent in continuous adsorption showed a low zone of mass transfer and high breakthrough time, indicating it to be an excellent material for fixed-bed operation. Overall, this study provides a low-cost and efficient alternative for the removal of dyes from aqueous solutions, with promising practical applications.

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In this study, coal bottom ash from a thermoelectric plant was tested as an alternative Fenton catalyst for phenol degradation in water. The effect of operating parameters such as initial pH, catalyst dosage and H2O2 concentration were evaluated. The characterization results indicated that the material has a mesoporous structure, with active species (Fe) well distributed on its surface. Under the optimal reaction conditions (6 mM H2O2, 1 g L-1 of catalyst and pH = 3), 98.7% phenol degradation efficiency was achieved in 60 min, as well as 71.6% TOC removal after 150 min. Hydroxyl radical was identified as the main oxidizing agent involved on the cleavage of the phenol molecule. After four consecutive reuse cycles, phenol degradation efficiency was around 80%, indicating good reusability and stability of the catalyst. Therefore, the obtained results demonstrated that the bottom ash presents remarkable activity for application in the Fenton reaction towards phenol degradation.

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In this work, a novel support for an iron-based catalyst was prepared and employed for Ponceau 4R degradation by photo-Fenton reaction. To this, poultry waste was used for producing char, which was subsequently used to prepare the Fe2O3/Char composite. Process parameters, including catalyst dosage, pH, and hydrogen peroxide concentration, were investigated. The characterization analysis indicated that the textural properties of the composite were improved after impregnation with Fe2O3. The composite exhibited excellent catalytic activity, achieving a decolorization efficiency of 97% at 45 min and 81.06% organic carbon removal at 300 min. In addition, the material showed acceptable performance after four consecutive cycles. Furthermore, a scavenger test was performed to investigate the major reactive species involved in the Ponceau 4R oxidation, and a plausible mechanism for the respective reaction was projected. Therefore, the results of this research demonstrate that this material can be used as a potential catalyst for the abatement of dyed molecules from wastewater.

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In this work, CoFe2O4/TiO2 nanostructure was prepared through a facile and effective solvothermal route for efficient use in the degradation of the Erionyl Red A-3G model pollutant under ultraviolet irradiation. Characterization analysis indicated the successful heterojunction among the precursors. The composite presented band gap value of 2.75 eV, being smaller than that of the pristine TiO2, as well as mesoporous structure. The catalytic activity of nanostructure was investigated by employing a 22 factorial experimental design with 3 central points. The optimized reaction conditions were set as pH = 2 and catalyst dosage = 1.0 g L-1 for an initial pollutant concentration of 20 mg L-1. The prepared nanohybrid presented remarkable catalytic activity, reaching color removal efficiency of 95.39% after 15 min, as well as total organic carbon (TOC) removal of 69.4% after 120 min. The kinetic studies of TOC removal followed the pseudo-first order model, with a rate constant of 0.10 min-1. Moreover, the nanostructure presented magnetic behavior, being easily separated from the aqueous medium through the use of a simple external magnetic field.

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Using groundwater for human consumption is an alternative for places with no nearby surface water resources. Fluoride is commonly found in groundwater, and the consumption of this water for a prolonged time in concentrations that exceed established limits by WHO and Brazilian legislation on water potability (1.5 mg L-1) can cause harmful problems to human health. For this reason, fluoride removal is an important step before water consumption. In this work, activated alumina was impregnated with Fe-Al-La composite and employed for the first time as an adsorbent for fluoride removal from an aqueous environment. XRD, SEM/EDS, FT-IR, and point of zero charge were used to characterize the prepared adsorbent. The adsorptive performance of adsorbent material was investigated by employing a 23-central composite design (CCD), and the obtained experimental conditions were pH = 6.5 and adsorbent dosage = 3.0 g L-1. A maximum adsorption capacity of 8.17 mg g-1 at 298 K and pH = 6.5 was achieved by Langmuir isotherm to describe the adsorption. The kinetic model that better described experimental data was Avrami, with the kav parameter increasing with the initial concentration from 0.076 to 0.231 (min-1)nav. The nature of adsorption was found to be homogeneous, and it occurs in a monolayer. The fluoride removal performance for the prepared adsorbent was higher than granular activated alumina, showing that supporting Fe-Al-La at the alumina surface increased its fluoride adsorption capacity from 16 to 42% at the same experimental conditions. Finally, the influence of co-existing ions Cl-, SO42-, and NO3- was evaluated in fluoride adsorption, and the material presented great selectivity to fluoride. Thus, Fe-Al-La/AA adsorbent is a promising material for fluoride removal from water.

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Geopolymers were obtained from ashes through an alternative geopolymerization process and applied to remove Ni2+, Cu2+, Co2+, and Ag+ from synthetic aqueous media and real effluents. The study in synthetic solutions revealed that pseudo-second-order and general order models were the best to fit the kinetic curves. To represent the equilibrium curves, Langmuir and Freundlich were the most adequate. The geopolymer derived from bottom ash (GHA) was superior to adsorb Cu+2, Co+2, and Ag+1 than the geopolymer derived from fly ash (GFA). GHA reached adsorption capacities of 279.5, 288.2, and 462.8 mg g-1 for Co+2, Cu+2, and Ag+1, respectively. Otherwise, GFA was the best for Ni+2 removal, with an efficiency of 95% in low concentrations. In treating real effluents of the E-coat printing process, both GHA and GFA were efficient, with the removal of higher than 85% for all the metals. In brief, it can be stated that GFA and GHA prepared are promising materials to remove metals from aqueous media (synthetic and real), presenting fast adsorption kinetics, high adsorption capacity, and high metal removal percentage.

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Pharmaceutical compounds are a serious problem in the environment. They cause damage to the aquatic, animal, and human organisms and soon became considered emerging pollutants where their removal is extremely urgent. Among the techniques used, adsorption has been used with success, where several adsorbent materials, including those from residual biomass, have been used to remove these pollutants. In this study, the skins of the pitaya fruit (Hylocereus undatus) productive chain were carbonized with ZnCl2 to obtain activated carbon and later used in the adsorption of the drug naproxen (NPX) in a batch system. The Freundlich model demonstrated a better adjustment for the equilibrium isotherms. A high adsorption capacity for NPX (158.81 mg g-1) was obtained at 328 K, which can be attributed to the remarkable textural properties of the adsorbent, besides certain functional groups present on its surface. Thermodynamic studies confirmed the endothermic nature of the adsorption process (∆H0 = 0.2898 kJ mol-1). The linear driving force model (LDF) presented a good statistical adjustment to the experimental kinetic data. The application of the material in the treatment of simulated wastewater composed of various pharmaceutical drugs and salts was very promising, reaching 75.7% removal. Therefore, it can be inferred that the application of activated carbon derived from pitaya bark is highly promising in removing the NPX drug and treating synthetic mixtures containing other pharmaceutical substances.

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In this work, buckwheat husks (Fagopyrum esculentum) were modified by acid treatment and posteriorly employed to remove the ketoprofen in batch adsorption. The characterization results indicated that a more irregular surface with new empty spaces was generated after acid treatment. The adsorptive process was favored at acidic pH = 3. The dosage of 0.85 g L-1 was fixed for the kinetic and isothermal tests, obtaining good removal and capacity indications. The kinetic studies were better represented by pseudo-second-order, obtaining an experimental capacity of 74.3 mg g-1 for 200 mg L-1 of ketoprofen. An increase in temperature negatively affected the adsorption isotherm curves, resulting in a maximum capacity of 194.1 mg g-1. Thermodynamic results confirmed the exothermic nature of the process with physical forces acting. The adsorbent presented high efficiency in treating a synthetic effluent containing different drugs and salts, 71.2%. Therefore, adsorbent development from buckwheat husks treated with a strong acid is an excellent alternative, given the good removal results and the low cost for its preparation.

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Activated carbon prepared from grape branches was used as a remarkable adsorbent to uptake naproxen and treat a synthetic mixture from aqueous solutions. The material presented a highly porous texture, a surface area of 938 m2 g-1, and certain functional groups, which were key factors to uptake naproxen from effluents. The maximum adsorption capacity predicted by the Langmuir model for naproxen was 176 mg g-1. The thermodynamic study revealed that the adsorption process was endothermic and spontaneous. The linear driving force (LDF) model presented a good statistical adjustment to the experimental decay data. A suitable interaction pathway of naproxen adsorption onto activated carbon was proposed. The adsorbent material was highly efficient to treat a synthetic mixture containing several drugs and salts, reaching 95.63% removal. Last, it was found that the adsorbent can be regenerated up to 7 times using an HCl solution. Overall, the results proved that the activated carbon derived from grape branches could be an effective and sustainable adsorbent to treat wastewaters containing drugs.

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Schizolobium parahyba species can be found in all of South America, producing several residues that can be a major opportunity to develop activated carbon. This work presents the investigation regarding the development of a high specific surface activated carbon (981.55 m2 g-1) and its application in the adsorption of ketoprofen from the aqueous media. The ketoprofen molecules were better adhered to the adsorbent surface under acidic conditions (pH = 2), being the ideal adsorbent dosage determined as 0.7 g L-1, resulting in satisfactory values. It was found that the system reached equilibrium in 200 to 250 min depending on the initial concentration studied, achieving an adsorption capacity of 229 mg g-1. The general order was the most suitable model for describing the experimental data, with an R2 ≥ 0.9985 and MSR ≤ 63.40 (mg g-1)2. The equilibrium adsorption found that the temperature increases the adsorption capacity, achieving 447.35 mg g-1 at 328 K. Besides that, the Tóth model was the most suitable for describing the isotherms R2 ≥ 0.9990 and MSR ≤ 25.67 (mg g-1)2, indicating a heterogeneous adsorbent. The thermodynamic values found that the adsorption of ketoprofen is spontaneous (average ΔG0 of - 32.79 kJ mol-1) and endothermic (ΔH0 10.44 kJ mol-1). The treatment of simulated effluent with the developed adsorbent was efficient, removing 90% of ketoprofen, ibuprofen, and salts. It was found that the adsorbent is reaming its adsorption capacity up to the 5th cycle, progressively decreasing the adsorption capacity until the adsorption does not occur past the 12th cycle. Overall, the results demonstrated that the activated carbon from residual biomass of the Schizolobium parahyba species could be an excellent alternative in obtaining an effective adsorbent to treat wastewater-containing drugs.

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A series of geopolymers were synthesized from fly and bottom ashes of a thermoelectrical power plant located in the Brazilian southern, aiming to add value for these wastes. The geopolymers were prepared in conventional and ultrasound-assisted ways and used to uptake Ag+, Co2+, Cu2+, and Ni2+ from aqueous solutions. All materials were characterized by infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and N2 adsorption isotherms (BET and BJH methods). The results revealed that the geopolymers obtained from the conventional method presented slightly higher values of surface area and total pore volume. However, in some cases, the adsorption potential was better for the ultrasound synthesized materials. The geopolymers prepared from both methods presented good adsorption performance concerning Ag+ and Cu2+, Co2+ and Ni2+. The removal percentages were higher than 90%. In addition, the adsorption capacities were within the literature range. These findings show that the ultrasound technique is not essential to improve the geopolymers production process compared to the conventional process, which generated material with better performance for heavy metals adsorption. Besides, it was possible to aggregate value for fly and bottom ashes, generating promising adsorbent materials.

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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.

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In this work, coal bottom ash was modified by alkaline fusion route in order to improve its pore properties and make it a potential adsorbent to remove crystal violet dye from aqueous medium. The solids were characterized and posteriorly subjected to kinetic, isotherm, and thermodynamic studies, as well as regenerated and reused for five adsorption tests. The alkaline fusion step resulted in the amorphization of material and generation of high surface area (102 m 2 g -1) and pore volume (0.180 cm 3 g-1), resulting in superior performance compared to the raw material. Kinetic and equilibrium studies showed that the adsorption process was better adjusted by the pseudo-second order and Langmuir models, respectively. The maximum adsorption capacity at equilibrium was 177. 37 mg g-1, with the adsorptive step occurring spontaneously and endothermically. The adsorbent maintained notable levels of dye removal after five consecutive cycles of thermal regeneration and reuse. Besides, the adsorbent was able to remove 64% of the colour of simulated industrial wastewater. Therefore, the alkaline fusion step proved to be a route capable of transforming the coal bottom ash into an adsorbent with improved textural and adsorptive properties.

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In this work, a novel and effective hydrochar was prepared by hydrothermal treatment of Prunus serrulata bark to remove the pesticide atrazine in river waters. The hydrothermal treatment has generated hydrochar with a rough surface and small cavities, favoring the atrazine adsorption. The adsorption equilibrium time was not influenced by different atrazine concentrations used, being reached after 240 min. The Elovich adsorption kinetic model presented the best adjustment to the kinetic data. The Langmuir model presented the greatest compliance to the isotherm data and indicated a higher affinity between atrazine and hydrochar, reaching a maximum adsorption capacity of 63.35 mg g-1. Thermodynamic parameters showed that the adsorption process was highly spontaneous, endothermic, and favorable, with a predominance of physical attraction forces. In treating three real river samples containing atrazine, the adsorbent showed high removal efficiency, being above 70 %. The hydrochar from Prunus serrulata bark waste proved highly viable to remove atrazine from river waters due to its high efficiency and low precursor material cost.

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The residual bark of the tree species Campomanesia guazumifolia was successfully modified with H2SO4 and applied to remove the toxic herbicide 2.4-dichlorophenoxyacetic (2.4-D) from aqueous solutions. The characterization techniques made it possible to observe that the material maintained its amorphous structure; however, a new FTIR band emerged, indicating the interaction of the lignocellulosic matrix with sulfuric acid. Micrographs showed that the material maintained its irregular shape; however, new spaces and cavities appeared after the acidic modification. Regardless of the herbicide concentration, the system tended to equilibrium after 120 min. Using the best statistical coefficients, the Elovich model was the one that best fitted the kinetic data. The temperature increase in the system negatively influenced the adsorption of 2.4-D, reaching a maximum capacity of 312.81 mg g-1 at 298 K. The equilibrium curves showed a better fit to the Tóth model. Thermodynamic parameters confirmed the exothermic nature of the system (ΔH0 = -59.86 kJ mol-1). As a residue obtained from urban pruning, the bark of Campomanesia guazumifolia treated with sulfuric acid is a promising and highly efficient alternative for removing the widely used and toxic 2.4-D herbicide from aqueous solutions.

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Produced water, a mixture of inorganic and organic components, comprises the largest effluent stream from oil and gas activities. The removal of contaminants from this wastewater is receiving special attention of the researchers since most of them are persistent and difficult to remove with simple techniques. Several technologies from conventional to advanced oxidation processes have been employed to treat produced water. However, the achievement of greater efficiency may be conditioned to a combination of different wastewater treatment techniques. Hereupon, the present paper discusses three important aspects regarding produced water treatment: analytical methods used for characterization, relevant aspects regarding photochemical systems used for advanced oxidation processes, and combined techniques for treating oil field wastewaters. Analytical methods employed for the quantification of the main species contained in produced water are presented for a proper characterization. Photochemical aspects of the reaction systems such as operating conditions, types of irradiation sources, and technical details of reactors are also addressed. Finally, research papers concerning combined treatment techniques are discussed focusing on the essential contributions. Thus, this manuscript aims to assist in the development of novel techniques and the improvement of produced water treatment to obtain a high-quality treated effluent and reduce environmental impacts.

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Real hospital wastewater was effectively treated by a promising technology based on degradation reaction catalyzed by Fe0 under microwave irradiation in this work. Fe0 powders were synthesized and characterized by different techniques, resulting in a single-phase sample with spherical particles. Optimum experimental conditions were determined by a central composite rotatable design combined with a response surface methodology, resulting in 96.8% of chemical oxygen demand reduction and 100% organic carbon removal, after applying MW power of 780 W and Fe0 dosage of 0.36 g L-1 for 60 min. Amongst the several organic compounds identified in the wastewater sample, diclofenac and ibuprofen were present in higher concentrations; therefore, they were set as target pollutants. Both compounds were completely degraded in 35 min of reaction time. Their plausible degradation pathways were investigated and proposed. Overall, the method developed in this work effectively removed high concentrations of pharmaceuticals in hospital wastewater.

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A new alternative aerogel was prepared from low-cost chitin and psyllium biopolymers to adsorb crystal violet (CV) dye from liquid media and possibly treat effluents containing other dyes. The aerogel was characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), which demonstrated that aerogel has a typical structure of amorphous materials and presented a randomly interconnected porous structure that resembles an open pore network. 2.5 g L-1 of aerogel was able to remove 86.00% of CV from solutions, and the natural pH of the CV solution was considered the more adequate for adsorption. The pseudo-second-order (PSO) model satisfactorily described the adsorption kinetics, and the Freundlich model was suitable to represent the adsorption equilibrium. The maximum experimental capacity achieved was 227.11 mg g-1, which indicates that aerogel is very efficient and competitive with several adsorbents. Tests using a simulated effluent showed that aerogel has excellent potential to treat real colored effluents.

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In this work, peanut (Arachis hypogaea) skin, a by-product generated by the agricultural production of its seeds, was employed as a precursor in the preparation of an adsorbent for the 2,4-D removal in water. The skins were treated with sulfuric acid and characterized by different techniques. The adsorption was favored at acid pH = 2 with pHpzc = 6. The dosage of 0.9 g L-1 was considered ideal, obtaining satisfactory indications of removal and capacity. The kinetic curves were well represented by the general order model, with the equilibrium reached quickly in the first 30 min for all concentrations. Adsorption isotherm studies showed that the increase in temperature negatively affected the herbicide adsorption, obtaining a maximum capacity of 246.72 mg g-1, by the Langmuir isotherm at 298 K. The remarkable adsorption efficiency presented by the adsorbent can be associated with the presence of new functional groups on the adsorbent surface generated after the acid treatment. Thermodynamic parameters confirmed the exothermic nature of the adsorptive system. In the treatment of synthetic wastewater consisting of a mixture of herbicides and salts, a high removal efficiency (72%) of herbicides was obtained. Therefore, the development of an adsorbent derived from peanut (Arachis hypogaea) skin treated with sulfuric acid is an excellent alternative, generating remarkable removal results towards 2,4-D herbicide.

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