Natural Zeolite Clinoptilolite Application in Wastewater Treatment: Methylene Blue, Zinc and Cadmium Abatement Tests and Kinetic Studies

Fundamental properties and sustainable applications of the natural zeolite clinoptilolite

This review explores a set of sustainable applications of clinoptilolite, a natural zeolite abundant around the world in different localities. Thanks to its physico-chemical properties this material is extremely versatile for several applications, ranging from environmental catalysis and CO2 removal to industrial and agricultural wastewater purification, aquaculture, animal feeding, and food industry but also medical applications and energy storage systems. Due to the presence of cations in its framework, it is possible to tune the material's features making it suitable for adsorbing specific compounds. Thus, this review aims to provide insight into developing new technologies based on the use of this material that is sustainable, not harmful for humans and animals, naturally abundant, and above all cost-effective. Furthermore, it is intended to promote the use of natural materials in various areas with a view to sustainability and to reduce as far as possible the use of chemicals or other materials whose synthesis process can have a polluting effect on the environment.

Mesoporous TiO2 and Fe-containing TiO2 prepared by solution combustion synthesis as catalysts for the photodegradation of paracetamol

Water pollution due to emerging contaminants, e.g., pharmaceuticals, is one of the most frequently discussed issues. Among them, paracetamol received great attention due to its physico-chemical properties, persistence, and adverse environmental effects. Different techniques were employed for its degradation and, among them, photodegradation is considered one of the most suitable to pursue the aim. This work aimed to synthesize mesoporous TiO2, even with the presence of iron, through a one-pot method, with an enhanced ability to abate paracetamol. Precisely, pure and iron-containing (3.5 wt%) TiO2 were successfully obtained employing an uncommon procedure for this kind of material, mainly solution combustion synthesis (SCS). Moreover, a traditional hydrothermal method and a commercial Degussa P25 were also investigated for comparison purposes. The samples were characterized through N2-physisorption at - 196 °C, XRD, XPS, EDX, DR UV-Vis, and FESEM analysis. The catalytic activity was investigated for the abatement of 10 ppm of paracetamol, under UV irradiation in acidic conditions (pH = 3) and in the presence of H2O2. As a whole, the best-performing catalysts were those obtained through the SCS procedure, highlighting a complete removal of the organic pollutant after 1 h in the case of Fe/TiO2_SCS, thanks to its highly defective structure and the presence of metal Fe. To better investigate the performance of both pure and Fe-containing SCS samples, further oxidation tests were performed at pH = 7 and in the absence of H2O2. Noteworthy, in these conditions, the two samples exhibited different behaviors, highlighting different mechanisms depending on the presence or absence of iron in the structure. Finally, a kinetic study was conducted, demonstrating that a first order is suitable for its abatement.

An Investigation of a Natural Biosorbent for Removing Methylene Blue Dye from Aqueous Solution

T he current study reports the use of zeolite prepared from a kaolin composite via physical mixing with different ratios from fiber of palm tree (Zeo-FPT) as a sustainable solid sorbent for the removal of methylene blue (MB) dye from aqueous solutions. The prepared biosorbent was fully characterized using XRD, TGA, SEM, and FTIR. The impacts of various analytical parameters, for example, contact time, dosage, MB dye concentration, and the pH of the solution, on the dye adsorption process were determined. After a contact time of 40 min, the capacity to remove MB dye was 0.438 mg g−1 at a Zeo-FPT composition ratio of 1F:1Z. At pH 8, Zeo-FPT (1F:1Z) had a removal efficiency of 87% at a sorbent dosage of 0.5 g for a concentration of MB dye in an aqueous phase of 10 mg L−1. The experimental data were also analyzed using the kinetic and adsorption isotherm models. The retention process fitted well with the pseudo-second-order model (R2 0.998), where the Qe,calc of 0.353 mg g−1 was in acceptable agreement with the Qe,exp of 0.438 mg g−1. The data also fitted well with the Freundlich isotherm model, as indicated by the correlation coefficient value (R2 0.969). The Zeo-FPT attained a high percentage (99%) in the removal of MB dye from environmental water samples (tap water, bottled water, and well water). Thus, it can be concluded that the proposed zeolite composite with fiber of palm tree (Zeo-FPT) is a suitable, environmentally friendly, and low-cost adsorbent for removing dyes from wastewater.