Wastewater-containing dyes are an environmental problem. The prime source of dye pollutants is the textile industry, such as paper manufacturing, food processing, leather, pigments, etc. Dye removal from wastewater using nanotechnology has received attention in recent decades thanks to efficient nanomaterials improving traditional technologies. In recent years, multiple research reports on carbon nanotubes for dye removal and photocatalytic dye degradation provided substantial insight into the comprehension of nanotechnology and remediation. This work presents a review and bibliometric analysis of carbon nanotubes for dye removal and photocatalytic dye degradation, which have an environmental impact today. The bibliometric study showed that the current research tendency on carbon nanotubes applied in dye removal and photocatalysis is still growing. According to research, this work observed that carbon nanotubes for dye removal exhibit high removal and efficient photocatalysis activity, indicating the functionality of nanotechnology for environmental remediation. The analysis of the parameters involved in the removal studies, such as temperature and pH, showed adsorption behavior. The photodegradation of methylene blue demonstrated the photocatalytic activity of carbon nanotubes attributed to the sp² lattice of graphitic configuration.

This work presents the synthesis of Au nanoparticles from gold coatings recovered from processor pins with minimal waste generation. The process consisted of four main steps: (1) physical recovery of pins, (2) recovery of gold coatings by acid digestion, (3) synthesis of HAuCl₄ under mild conditions and, (4) synthesis of Au nanoparticles by the Turkevich method. The small dimensions of Au coatings allowed the synthesis of HAuCl₄ with lower amounts of HCl_conc and HNO_3conc than those used with aqua regia. This method has significant advantages, such as lower NO_2(g) emission, easy post-treatment and purification, low synthesis cost and high yields. Gold nanoparticles synthesized from HAuCl₄ were characterized by transmission electron microscopy (TEM) and UV-Vis spectroscopy. Size distribution analysis showed particles 14.23 nm in length and 12.05 nm in width, while absorption spectra showed a surface plasmon located at 523 nm; these characteristics were very similar to those observed with Au nanoparticles obtained with Aldrich’s reagent. It is suggested that recycling procedures can be improved by taking into account the size and shape of the metals to be recovered, thus introducing a new field of research known as hydronanometallurgy.

This study investigates the potential of using gold nanoparticles (Au NPs) synthesized from e-waste as electrocatalysts for the methanol oxidation reaction (MOR), with the aim of applying them as an anode in alkaline direct methanol fuel cells (ADMFCs). The research addresses the pressing environmental challenge of e-waste disposal and explores the recycling of e-waste to obtain valuable materials for sustainable applications. Vulcan-supported gold nanoparticles (Au_e-w/C NPs) are synthesized from gold coatings recovered from Intel Pentium 4 processor pins, demonstrating the feasibility of e-waste as electrocatalyst precursors. Comprehensive characterization techniques such as UV-Vis spectroscopy, high-resolution transmission and transmission electron microscopy (HR-TEM, TEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), and X-ray diffraction (XRD) are employed to evaluate the structural properties of the electrocatalyst. Electrochemical evaluation in 0.5 M KOH electrolyte by cyclic voltammetry reveals that the synthesized Au_e-w/C NPs exhibit electrocatalytic activity (25.5 mA·mg⁻¹_Au) comparable to their commercially synthesized counterparts (30.1 mA·mg⁻¹_Au). This study highlights the potential for sustainable approaches in the production of electrocatalysts by utilizing e-waste as a source of valuable catalyst materials. It represents a pioneering effort in harnessing e-waste as a sustainable resource, offering new avenues for sustainable energy technologies while addressing environmental concerns and technological challenges in the field of ADMFCs.