Lindemberg de Jesus Nogueira Duarte

The need to mitigate environmental pollution and the risks to human health posed by heavy metal contamination of water resources are among the main anthropogenic challenges. Although the analytical techniques used to detect and quantify metal ions are effective and well established, they still require complex and expensive instrumentation. Detection techniques based on colorimetric chemosensors have emerged as a simple and efficient alternative for on‐site analysis of metal ions. The aim of this study was to investigate the performance of sodium levulinate (NaLev) as an organic molecular sensor in a spectrophotometric procedure for the colorimetric detection of copper ions (Cu ²⁺ ) in aqueous solution. To this end, NaLev was first synthesized by hydrating levulinic acid with distilled water, using 18.5 mL of levulinic acid and 20 mL of distilled water, with the addition of 20 g of sodium hydroxide. The concentrations of Cu ²⁺ , NaLev, and the Cu ²⁺ –NaLev complex were determined by molecular absorption spectroscopy in the ultraviolet–visible (UV–Vis) region. The results showed that the addition of NaLev led to a significant increase in absorbance, accompanied by a gradual decrease in wavelength from 810 to 575 nm in samples without and with NaLev, respectively. The colour intensity of the Cu ²⁺ solution increased as the NaLev concentration rose. Concentrations as low as approximately 1 ppm, or even lower, could be detected using the proposed method. Thus, the NaLev colorimetric sensor for detecting Cu ²⁺ ions appears to represent a promising class of biologically based, heavy‐metal‐free colorimetric sensors.

Investigating viable processes for the use of lignocellulosic biomass in clean fuels and high-value-added chemical products is essential for sustainable development. Large amounts of lignin are available every year as by-products of the paper and biorefinery industries, causing a series of problems, particularly environmental ones. Its structure and composition make lignin compatible with the concept of sustainability, since it can be used to produce new chemical products with high added value. As such, this study aims to extract lignin from green coconut fiber (LIG), with the subsequent impregnation of a sodium-octanoate-based surfactant (LIG-SUR), and determine its applicability as an adsorbent for removing copper ions from synthetic waste. To this end, the green coconut fiber lignocellulosic biomass was initially subjected to alkaline pre-treatment with 2% (w/v) sodium hydroxide in an autoclave. Next, the surface of the lignin was modified by impregnating it with sodium octanoate, synthesized from the reaction of octanoic acid and NaOH. The physical and chemical traits of the lignin were studied before and after surfactant impregnation, as well as after copper ion adsorption. The lignin was analyzed by X-ray fluorescence (XRF), Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). The adsorption tests were carried out using lignin pre-treated with surfactant in a batch system, where the effects of pH and adsorbent concentration were investigated. XRF and SEM analyses confirmed surfactant impregnation, with Na₂O partially replaced by CuO after Cu²⁺ adsorption. FTIR analysis revealed shifts in O–H, C–H, C=O, and C=C bands, indicating electrostatic interactions with lignin. Adsorption kinetics followed the pseudo-second-order model, suggesting chemisorption, with equilibrium reached in approximately 10 and 60 min for LIG-SUR and LIG, respectively. The Langmuir model best described the isotherm data, indicating monolayer adsorption. LIG-SUR removed 91.57% of Cu²⁺ and reached a maximum capacity of 30.7 mg·g⁻¹ at 25 °C and a pH of 6. The results of this research showed that pre-treatment with NaOH, followed by impregnation with surfactant, significantly increased the adsorption capacity of copper ions in solution. This technique is a viable and sustainable alternative to the traditional adsorbents used to treat liquid waste. In addition, by using green coconut fiber lignin more efficiently, the research contributes to adding value to this material and strengthening practices in line with the circular economy and environmental preservation.

The use of low-cost, widely available environmental friendly catalysts may strengthen the sustainability of lignocellulosic biomass conversion into levulinic esters. In this respect, the present study aimed to optimize the methyl esterification reaction between levulinic acid (LVA) and aluminum sulfate [Al₂(SO₄)₃] with a view to producing methyl levulinate (MLV). The Box–Behnken design for three factors was applied to investigate the influence of reaction time (60, 120, and 180 min), alcohol:acid molar ratio (4:1, 8:1, and 12:1), and catalyst concentration (0.02, 0.04, and 0.06 mol L⁻¹) on LVA conversion into MLV. The reactions occurred in a Parr Instruments stainless steel reactor, at a temperature of 140 ºC and 733 rpm rotation. The results indicated that the interaction between molar ratio and catalyst concentration has a significant influence on LVA conversion. The regression model obtained is significant and predictive, with an R² value of 0.86. Analyses of response surfaces showed that a 60 min reaction time produces high conversion, irrespective of the amount of catalyst. Fixing the shortest reaction time and lowest Al₂(SO₄)₃ concentration, the molar ratio indicated for the reaction would be 1:6. The levels selected provide conversions varying from 86.83% to 99.27%, demonstrating the efficiency of a low-cost catalyst at low concentrations.

Increasing concern about climate change and the need to reduce dependence on fossil fuels have driven the search for more sustainable energy alternatives. One way to reduce emissions is by adding oxygenated compounds such as biodiesel and alcohols to diesel fuel. However, this can lead to phase separation between the fuels and have serious consequences for engine performance. In this context, the present study aimed to evaluate the effect of ethanol content on the miscibility of components in mixtures containing ethanol + biodiesel + diesel through the study of liquid-liquid equilibrium. The results from ternary phase diagrams revealed that the amount of water present in ethanol has a significant effect on the miscibility of the mixture components, with larger biphasic regions observed in systems with lower ethanol content. For the 95% ethanol diagram, the reliability of experimental data on equilibrium lines was assessed through the Othmer-Tobias and Hand correlations, which showed correlation coefficients (R²) of 0.996 and 0.995, respectively. The results obtained from the NRTL and UNIQUAC thermodynamic models demonstrated excellent agreement with the experimental data, with a deviation of only 1.78 and 0.78% for the NRTL and UNIQUAC models.

Liquid-liquid equilibrium data were measured and analyzed for two ternary systems (biodiesel + methanol + glycerol and methyl palmitate + methanol + glycerol). Biodiesel, produced by the conventional chemical route at 60 °C for 60 min, using methanol and soybean oil at a molar rate of 10:1 and potassium hydroxide concentration (KOH) of 1 wt% exhibited thermal decomposition at temperatures between 100 and 250 ºC, reaching mass loss of approximately 98.8%, confirming soybean oil conversion into biodiesel by gas chromatography and thermogravimetry. Tie line composition quality was verified using Othmer-Tobias and Hand correlation equations. The distribution and selectivity coefficients were calculated for the immiscibility regions. The experimental tie line data exhibited good correlation in the UNIQUAC and NRTL thermodynamic models. The biodiesel system displayed deviations of 0.66 and 0.53% for the UNIQUAC and NRTL models, respectively. In addition, the methyl palmitate system showed a 1.23 and 0.48% deviation for the UNIQUAC and NRTL model, respectively. The individual behavior of the main biodiesel esters , based on the UNIQUAC model parameters, demonstrated that the type of fatty acid does not interfere in model correlation, likely due to the similarity between their composition and properties.

The impacts of inadequate disposal of industrial wastewater cause environmental, economic, social and human health damage. The search for innovative and viable methodologies from a technical and economic standpoint aims to promote suitable management of effluents produced by different industrial activities. The objective of this paper was to study phenol, aromatic alcohol and aromatic amine removal using cloud point extraction based on analysis of extraction capacity, miscibility curves, equilibrium lines, distribution coefficients and mass transfer solubilisation diffusion. The oxo-C₁₀E₃P₄E₂ surfactant produced the best results, exhibiting smaller coacervate volume fractions, low concentration in the diluted phase and efficient extraction (E%) of phenol (81.79%), 1-phenylethanol (67.88%), 2-phenylethanol (65.41%), benzyl alcohol (57.01%), aniline (56.91%), p-toluidine (73.96%) and 2,4-dimethylaniline (84.87%). The ternary phase diagrams revealed a large miscibility area favourable to extraction, with equilibrium lines showing a pronounced slope in favour of the coacervate, indicating high compound concentration factors. Equilibrium isotherms were used to obtain the distribution and solubilisation constants (Log K_C/D K_S), in the following order: aniline (1.05; 9.15) < p-toluidine (1.35; 20.40) < 2,4-dimethylaniline (1.76; 45.10) and benzyl alcohol (1.07; 8.19) < 2-phenylethanol (1.22; 14.04) < 1-phenylethanol (1.28; 15.23) < phenol (1.59; 36.72). These parameters show a linear correlation with Log K_O/W, revealing that micellar solubilisation is governed by the hydrophobic nature of aromatic organic compounds. The evolution of pH demonstrated that the ionised forms of phenol and 2,4-dimethylaniline do not establish interactions (electrostatic, van der Waals, hydrogen bonds) with surfactants. Mass transfer diffusion is governed by hydrophobic compounds, slightly compromising phenol due to its high solubility in water.

Diclofenac is a highly toxic anti-inflammatory detected in effluents and wastewater treatment plants. Adsorption is one of the most widely applied technologies to remove micropollutants using activated carbon, but requires a costly and inefficient separation stage, compromising adsorption. In this respect, a novel process is proposed based on ionic micellar flocculation-assisted adsorption (IMFA) using the surfactant sodium dodecanoate to increase adsorption capacity and facilitate phase separation. The efficiency of adsorption and IMFA was assessed based on a kinetic study, equilibrium isotherms, thermodynamic and kinetic separation properties. Adsorption kinetics followed the pseudo-second model indicating a process governed by ionic exchange between sodium diclofenac and the ions present in the activated carbon layers and dodecanoate, with velocity constants of 8.51 and 5.24 g.mg⁻¹.min⁻¹, respectively. Based on the equilibrium isotherms, the maximum adsorption capacity obtained was 49.43 and 51.85 mg.g⁻¹ in adsorption and IMFA, respectively, best represented by the Langmuir adsorption model, assuming adsorption on homogeneous surfaces in the form of monolayers. Thermodynamic analysis revealed that the processes occurred spontaneously, exothermically and that randomness declines at the solid-solution interface. Sedimentation analysis showed that the higher the surfactant concentration the greater the compaction height, higher the decantation speed, and shorter the wastewater clarification time.

Emerging pollutants (EPs) have recently been reported to affect the quality of water and pose high risks to human health. The recalcitrant behavior of the drug hydrochlorothiazide (HCT) in wastewater, for example, highlights the need to develop new treatments that are more efficient in removing this pollutant. In this study, the removal of hydrochlorothiazide from a synthetic pharmaceutical effluent through micellar ionic flocculation was evaluated, using a biodegradable anionic surfactant, derived from natural materials such as coconut oil and animal fat. The effects of different parameters, such as contact time, stirring speed, temperature, surfactant concentration and pH on drug removal efficiency were assessed. Under optimal processing conditions: [HCT] = 20 ppm, [surfactant] = 300 ppm, 1:2 calcium/surfactant ratio, temperature 30 °C, contact time 5 min, fast stirring speed 100 rpm, slow stirring speed 50 rpm and pH 10, HCT removal efficiency reached 88%, indicating that ionic flocculation using base soap is a promising technique in the treatment of pharmaceutical effluents contaminated by hydrochlorothiazide. The desorption kinetics of HCT from the floc surface were also analyzed, confirming that desorption is governed by the pseudo-second order, where interactions between the polar group of the base soap (COOH⁻), Ca⁺² ions and HCT (C₇H₈ClN₃O₄S₂) detach the HCT molecules present in the flocs. Moreover, 15% of HCT was spontaneously desorbed after 40 min. Graphical Abstract

The high global dependence on nonrenewable energies has prompted scientific studies aimed at developing new sources of renewable energy based on biofuel production. The biodiesel used in diesel engines has been one of the viable alternatives to mitigate the problems resulting from the use of fossil fuels. The industrial production of this biofuel uses basic homogeneous catalysts, but problems related to the high cost of purifying the product and waste generation, among others, are common. These complications have led to the development of a heterogeneous catalyst, which has proved to be a good option for biodiesel production. In this respect, the aim of the present study was to formulate and assess heterogeneous catalysts derived from chicken egg shells and diatomite for biodiesel production. Initially, the egg shell was calcined, forming CaO, followed by wet impregnation with diatomite via calcination at 800 °C for 240 min, producing the catalyst DiaCaO. The catalysts were characterized by XRD, FTIR, SEM, BET and XRF analyses, which confirmed the formation of catalytic solids based on the composition and chemical structure. In relation to biodiesel production, the CaO and DiaCaO catalysts exhibited similar yields, with the CaO precursor converting around 99% into biodiesel under favorable conditions (6:1 methanol:oil molar ratio, 2% catalyst and 2 h reaction time).