Emerging pollutants such as butylparaben (BP) are often difficult to remove via conventional wastewater treatment. Therefore, this study aimed to produce and characterize graphene oxide (GO) and evaluate the adsorption of BP on this adsorbent. The GO was made using the Hummers method and characterized by TGA/DTA, XRD, XRF, BET, point of zero charge (pHpzc), SEM, and the Boehman method. Adsorption experiments were performed in a batch system. The removal efficiency from a Box–Behnken experimental design was 84.3% at a BP concentration 600 µg∙L⁻¹, adsorbent five g∙L^−1, and pH 7 in solution. The first-order (PFO) kinetics obtained the best fit to the experimental data compared to the other models tested in this study: pseudo-second-order (PSO), Elovich (ELC), and intra-particle diffusion (IPD). The Langmuir isotherm provided the best fit compared to the Freundlich isotherm. The temperature effect showed that the system has a spontaneous adsorption process, with a Gibbs energy lower than zero, and that increasing the temperature increases the adsorption capacity. The ionic effect showed that increasing the salt concentration of 1 M increased the repulsive forces but did not decrease the adsorption capacity. The regeneration cycle showed a rate of 85% up to the second cycle. The toxicity analysis confirmed the efficiency of the adsorption process using GO before and after BP adsorption on GO.

The development of dye-sensitized solar cells (DSSCs) has gained prominence as an economical alternative for photovoltaic energy conversion. This work investigates the synthesis of niobium pentoxide (Nb₂O₅) by the Pechini method, followed by calcination at different temperatures (500 °C, 600 °C and 700 °C) to evaluate its structural, morphological, and electrochemical properties as a photoanode material in DSSCs. SEM and XRD analyses revealed that calcination at 600 °C produced a material with optimized particle size (642.17 ± 37 nm) and adequate crystalline structure, favoring dye adsorption and electronic transport. Electrochemical characterization, including open-circuit potential and impedance spectroscopy, indicated that the sample at 600 °C presented superior photovoltaic performance, achieving a power conversion efficiency of 1.39% and electron lifetime equal to 0.159 s. These findings suggest that Nb₂O₅, under controlled calcination conditions, may act as a promising alternative to TiO₂ substitution in DSSC applications.

Superabsorbent polymers (PSAs) have been extensively studied to act as internal curing agents in cementitious materials, as they have the characteristic of absorbing and releasing water in a controlled manner, which can contribute to the hydration process of a cementitious medium during its consolidation. Thus, hydrogels consisting of polyacrylamide (PAAm), pectin (Pec) and rice husk ash (RHA) were synthesized to be applied in cementitious matrices. In addition, the PSAs were characterized by FTIR, SEM, and XRD. For evaluating the usage of hydrogels as internal curing agents, different hydrogel contents—0.03, 0.06, and 0.1 (wt-%, relative to cementitious components)—were used for mortar preparation. The mechanical strengths of the cementitious materials were evaluated at day 7 and day 28 during the curing process. The addition of PSAs to the mortars caused an increase in mechanical resistance such that the 0.06% content presented better performance at day 7 of curing (4.07% higher) and at day 28 of curing (8.06% higher) when compared with the reference mortar (without the addition of PSAs) in the same curing periods. This work demonstrates that the addition of PSAs contributes to the hydration of a cementitious material, improving the mechanical resistance of the studied mortars.

Internal curing is a process based on the addition of materials that function as water reservoirs in cementitious media. Superabsorbent hydrogels are an alternative that can be used as an internal curing agent, as they have the ability to absorb and release water in a controlled manner. In the present work, superabsorbent hydrogels based on crosslinked polyacrylamide in the presence of starch and sugarcane bagasse ash (SCBA) were developed and applied to mortars as an internal curing agent. The synthesized hydrogels were evaluated by SEM, FTIR, and swelling analysis. Cement pastes and mortars were produced using different amounts of hydrogel (0.03%, 0.06%, and 0.1% by weight). An analysis of the cement pastes and mortars revealed that hydrogel contributes to hydration, thus improving the quality of the product. Furthermore, the addition of 0.03% hydrogel by weight increased the mechanical resistance of the mortars in up to 26.8% at 28 days of curing as compared with reference (without hydrogel). To the best of our knowledge, this is the first study to use a hydrogel based on polyacrylamide crosslinked with starch and SCBA as a curing agent for mortars and cement pastes. This approach is environmentally friendly, because it uses a natural product (starch) and a byproduct from the sugarcane industry (SCBA).

Searching for sustainable alternatives to environmental challenges has driven significant interest in metal oxides, particularly TiO₂, due to its versatility in energy conversion, pollutant adsorption, and electrochemical applications. TiO₂ powders were synthesized via a modified Pechini method, comparing the conventional route with the use of the Tween-80 surfactant as a structure-directing agent. Structural, morphological, and electrochemical characterizations were performed to assess the impact of the synthesis on material performance. Thermogravimetric analysis (TG) revealed distinct decomposition profiles, with the Tween-based precursor exhibiting enhanced thermal stability. X-ray diffraction confirmed the formation of anatase–rutile structures, with Tween-80 favoring a higher anatase content (74.3% anatase phase). Scanning electron microscopy (SEM) and specific surface area (S_BET) measurements demonstrated that Tween-80 promoted a more porous and fragmented morphology, leading to a 21-fold increase in specific surface area. ζ potential and XRD–Rietveld analysis further elucidated the influence of the organic precursor on the surface charge and crystallite size. Electrochemical impedance spectroscopy (EIS) showed a significant reduction in charge transfer resistance (65.8 kΩ), compared to that of ethylene glycol-based films (943 kΩ), while cyclic voltammetry (CV) in the presence of methylene blue indicated improved redox activity, enhancing the applicability of this TiO₂ powder in several areas.