In the present study, Fe₃O₄/poly(2-hydroxyethyl methacrylate-co-itaconic acid) magnetic hydrogels (MHGs) were prepared by in situ synthesis of Fe₃O₄ magnetic particles in hydrogels (HGs). The resulting magnetic hydrogels were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), a vibrating sample magnetometer (VSM), scanning electron microscopy (SEM), and N₂ adsorption–desorption. The effect of Fe₃O₄ on the swelling behavior and adsorption of methylene blue (MB) dye of the prepared hydrogel was studied. Parameters such as the dose, pH, contact time, and MB initial concentration were investigated. The results show that 75% (HG) and 91% (MHG) of MB (200 mg/L) were removed at doses of 2 mg/mL and 1 mg/mL, respectively, under a pH of 6.8 and a contact time of 10 min. The adsorption behavior followed the Langmuir isotherm model, indicating that the adsorption process takes place in monolayers and on homogeneous surfaces. The Langmuir capacities for MB adsorption using the HGs and MHGs were 78 and 174 mg/g, respectively. The adsorption kinetics followed a pseudo-second-order kinetic model. In addition, thermodynamic studies carried out show that the adsorption process is spontaneous and endothermic. Adsorption–desorption studies indicate that the magnetic hydrogel can remove MB for four cycles with removal efficiencies above 90%. Therefore, a MHG is suitable as an alternative material for MB adsorption.

An increase in the production of cationic dyes is expected over the next decade, which will have an impact on health and the environment. This work reports an adsorbent hydrogel composed of poly(acrylic acid) [poly(AA)] and Fe₃O₄ particles, prepared by radical polymerization and in situ co-precipitation of Fe³⁺ and Fe²⁺. This Fe₃O₄/poly(AA) composite hydrogel was used to evaluate its potential for removing the cationic dyes methylene blue (MB) and crystal violet (CV) from aqueous solutions. Instrumental characterization of the hydrogel was performed by FTIR, XRD, TGA, VSM, and physicochemical analysis (swelling and response to changes in pH). The results show that the incorporation of Fe₃O₄ particles improves the adsorption capacity of MB and CV dyes to a maximum adsorption of 571 and 321 mg/g, respectively, under the best conditions (pH 6.8, dose 1 g/L, time 24 h). The adsorption data best fit the pseudo-first order (PFO) kinetic model and the Freundlich isothermal model, indicating mass transfer via internal and/or external diffusion and active sites with different adsorption potentials. Moreover, the thermodynamic analysis confirmed that the adsorption process was spontaneous and exothermic, with physisorption as the dominant mechanism. In addition, the Fe₃O₄/poly(AA) hydrogel is capable of removing 95% of the dyes after ten consecutive adsorption–desorption cycles, demonstrating the potential of hydrogels loaded with Fe₃O₄ particles for the treatment of wastewater contaminated with dyes.

This paper reports the successful development and application of an efficient method for quantifying Pb²⁺ in aqueous samples using a smartphone-based colorimetric device with an imprinted polymer (IIP). The IIP was synthesized by modifying the previous study; using rhodizonate, 2-acrylamido-2-methylpropane sulfonic acid (AMPS), N,N′-methylenebisacrylamide (MBA), and potassium persulfate (KPS). The polymers were then characterized. An absorption study was performed to determine the optimal conditions for the smartphone-based colorimetric device processing. The device consists of a black box (10 × 10 × 10 cm), which was designed to ensure repeatability of the image acquisition. The methodology involved the use of a smartphone camera to capture images of IIP previously exposed at Pb²⁺ solutions with various concentrations, and color channel values were calculated (RGB, YMK HSVI). PLS multivariate regression was performed, and the optimum working range (0–10 mg L⁻¹) was determined using seven principal components with a detection limit (LOD) of 0.215 mg L⁻¹ and R² = 0.998. The applicability of a colorimetric sensor in real samples showed a coefficient of variation (% RSD) of less than 9%, and inductively coupled plasma mass spectrometry (ICP–MS) was applied as the reference method. These results confirmed that the quantitation smartphone-based colorimetric sensor is a suitable analytical tool for reliable on-site Pb²⁺ monitoring.

In this study, poly(HEMA-PEGxMEM-IA) hydrogels were prepared by radical copolymerization of poly(ethylene glycol) methyl ether methacrylate (PEGxMEM), 2-hydroxyethyl methacrylate (HEMA), and itaconic acid (IA). The reaction was carried out in ethanolic solution using N,N′-methylenebisacrylamide (MBA) as a crosslinking agent and 1-hydroxycyclohexyl phenyl ketone (HCPK) as a photo-initiator. The poly(HEMA-PEGxMEM-IA) hydrogels (HGx) were evaluated as a delivery system for ursolic acid (UA), a phytochemical extracted from the plant Clinopodium revolutum, “flor de arena”. The hydrogels were characterized by Fourier-transform infrared spectroscopy (FTIR-ATR), Raman spectroscopy, X-Ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The swelling behavior was studied in buffer solutions from pH 2 to 10, specifically at pH 2.2 (gastric environment) and 7.4 (intestinal environment). It was found that the hydrogels studied showed sensitivity to pH. At pH 2.2, the degree of swelling for HG₅ and HG₉ hydrogels was 0.45 and 0.93 (g water/g hydrogel), respectively. At pH 7.4, the degree of swelling for HG₅ and HG₉ hydrogels was 1.97 and 2.64 (g water/g hydrogel), respectively. The SEM images show the variation in pore size as a function of pH, and the UA crystals in the pores of the hydrogels can also be observed. The in vitro UA release data best fit the Korsmeyer–Peppas kinetic model and the diffusion exponent indicates that the release mechanism is governed by Fickian diffusion.