Ana C. Estrada

Potentially toxic elements (PTEs) have been found in high levels in rainwater, highlighting the importance of removing them when the water is intended for domestic use. In this work, white bean peel was evaluated as sorbent for the removal of a mixture of PTEs from rainwater, namely Zn(II), Cu(II) and Pb(II). A uniform experimental design was used to evaluate the sorption and to optimize the removal process by response surface methodology. The biosorbent reduced the PTEs concentration in the solution, and their removal increased with the increase of the initial concentration and with time. The removal of Cu(II) and Pb(II) was affected by the pH of the solution since, at pH 7.0 for Cu(II), and at pH 5.6 and 7.0 for Pb(II), a decrease occurred in the removal. The optimal conditions for removal, 6 h of contact time between the sorbent and the solution, were applied to rainwater samples spiked with the mixture of PTEs and resulted in removals of 30–90% for Zn(II), 11–78% for Cu(II), and 11–97% for Pb(II), generally lower than those expected by the models, 91% for Zn(II) and 52% for Cu(II), highlighting that the rainwater matrix interferes with the removal of PTEs by peel. However, the white bean peel may be an alternative as sorbent to reduce Zn(II), Cu(II), and Pb(II) concentrations in rainwater, since it is a natural and sustainable material.

We reported here a one‐step chemical route to prepare nanocomposites comprising CuS nanophases supported on GO sheets with magnetic properties. The synthesis reported here combines such materials in single‐nanostructures that show morphological features well‐suited for wastewater treatment. The photocatalytic performance of CuS/GO nanocomposites was first investigated towards the removal of a common organic dye (rhodamine B) and sulfamethoxazole (SMX), which is an antibiotic considered a water contaminant of emerging concern. The RhB and SMX adsorption efficiency of CuS/GO and Fe₃O₄/GO/CuS hybrids, as well as of CuS particles, was significantly higher than GO or Fe₃O₄/GO. Overall, the CuS‐based magnetic and CuS/GO hybrids have shown the capacity to uptake more than 80 % of RhB or SMX, after 120 minutes. Under blue‐led irradiation, almost complete degradation of RhB was achieved in the presence of CuS/Fe₃O₄/GO, after 180 minutes; and higher than 85 % degradation of SMX, after 240 minutes of irradiation. The photocatalytic behaviour of nanocomposites was best described by the first–order kinetic model, for which k values for degradation of RhB and SMX followed the order: CuS/Fe₃O₄/GO>CuS/GO>CuS. The tricomponent CuS/Fe₃O₄/GO can be easily recovered after use and be reused maintain their high photocatalytic performance, thus providing a sustainable and cost‐effective hybrid solution for water treatment.

Bismuth vanadate (BiVO₄) has been investigated as a photocatalyst of great interest due to its ability to harvest photons efficiently in the visible spectral region. In addition, powdered BiVO₄ shows high photochemical stability, good dispersibility, and resistance to corrosion in oxidative conditions. Herein, we report the synthesis of monoclinic or tetragonal BiVO₄ particles using different methods, as well as the synthesis of hybrids materials through the combination of cobalt ferrite (CoFe₂O₄) and BiVO₄, and their application in the photodegradation of aqueous solutions of sulfamethoxazole (SMX) under simulated solar radiation. We demonstrate that high-crystallinity single-phase monoclinic BiVO₄ was synthesized fast and efficiently using a solid-state method and, in combination with magnetic CoFe₂O₄ particles, gives rise to a hybrid material that can be easily separated from the reaction medium, by applying an external magnetic field, without the need for further downstream treatments.

Heterogeneous semiconductor photocatalysis has received much interest because of its applications in important global energy and environmental challenges in a cost-effective sustainable way. The photocatalytic efficiency of semiconductor photocatalysts under solar irradiation has been pointed out by difficulties associated with low visible-light absorption range, fast recombination of photogenerated carriers, and low chemical stability in operational conditions. Graphitic materials have attracted great interest due to properties, such as high surface area, mechanical strength, and photochemical stability. Thus, their combination with metal sulfides, has been explored as promising strategies to produce new photocatalysts. These nanocomposites show great potential in photodegradation of contaminants of emerging concern (CEC), which might be detected in water sources, such as traces of Pharmaceutics and pesticides. Here, we briefly review fundamental principles photocatalysis in general, with the focus on the use of carbon-nanomaterials of distinct structural dimensionalities associated with nanocrystalline metal sulfides, envisaging their application as heterogeneous photocatalysts for water remediation. Key aspects concerning the photocatalyst properties, such as light absorption, charge separation and transfer, and stability, are also approached. Graphene and graphene derivatives have demonstrated great potential for increasing photogenerated charge-carrier separation and migration efficiency, as well as in extending the light absorption range and adsorption capacity.

Considering the increasing emergence of new contaminants, such as nanomaterials, mixing with legacy contaminants, including metal(loid)s, it becomes imperative to understand the toxic profile resulting from these interactions. This work aimed at assessing and comparing the individual and combined hepatotoxic and neurotoxic potential of titanium dioxide nanoparticles (TiO₂NPs 0.75–75 mg/L), cerium oxide nanoparticles (CeO₂NPs 0.075–10 μg/L), arsenic (As 0.01–2.5 mg/L), and mercury (Hg 0.5–100 mg/L) on human hepatoma (HepG2) and neuroblastoma (SH-SY5Y) cells. Viability was assessed through WST-1 (24 h) and clonogenic (7 days) assays and it was affected in a dose-, time- and cell-dependent manner. Higher concentrations caused greater toxicity, while prolonged exposure caused inhibition of cell proliferation, even at low concentrations, for both cell lines. Cell cycle progression, explored by flow cytometry 24 h post-exposure, revealed that TiO₂NPs, As and Hg but not CeO₂NPs, changed the profiles of SH-SY5Y and HepG2 cells in a dose-dependent manner, and that the cell cycle was, overall, more affected by exposure to mixtures. Exposure to binary mixtures revealed either potentiation or antagonistic effects depending on the composition, cell type and time of exposure. These findings prove that joint toxicity of contaminants cannot be disregarded and must be further explored.

Humans are typically exposed to environmental contaminants’ mixtures that result in different toxicity than exposure to the individual counterparts. Yet, the toxicology of chemical mixtures has been overlooked. This work aims at assessing and comparing viability and cell cycle of A549 cells after exposure to single and binary mixtures of: titanium dioxide nanoparticles (TiO₂NP) 0.75–75 mg/L; cerium oxide nanoparticles (CeO₂NP) 0.75–10 μg/L; arsenic (As) 0.75–2.5 mg/L; and mercury (Hg) 5–100 mg/L. Viability was assessed through water-soluble tetrazolium (WST-1) and thiazolyl blue tetrazolium bromide (MTT) (24 h exposure) and clonogenic (seven-day exposure) assays. Cell cycle alterations were explored by flow cytometry. Viability was affected in a dose- and time-dependent manner. Prolonged exposure caused inhibition of cell proliferation even at low concentrations. Cell-cycle progression was affected by TiO₂NP 75 mg/L, and As 0.75 and 2.5 μg/L, increasing the cell proportion at G0/G1 phase. Combined exposure of TiO₂NP or CeO₂NP mitigated As adverse effects, increasing the cell surviving factor, but cell cycle alterations were still observed. Only CeO₂NP co-exposure reduced Hg toxicity, translated in a decrease of cells in Sub-G1. Toxicity was diminished for both NPs co-exposure compared to its toxicity alone, but a marked toxicity for the highest concentrations was observed for longer exposures. These findings prove that joint toxicity of contaminants must not be disregarded.

Graphene-based materials are elective materials for a number of technologies due to their unique properties. Also, semiconductor nanocrystals have been extensively explored due to their size-dependent properties that make them useful for several applications. By coupling both types of materials, new applications are envisaged that explore the synergistic properties in such hybrid nanostructures. This research reports a general wet chemistry method to prepare graphene oxide (GO) sheets decorated with nanophases of semiconductor metal sulfides. This method allows the in situ growth of metal sulfides onto GO by using metal dialkyldithiocarbamate complexes as single-molecule precursors. In particular, the role of GO as heterogeneous substrate for the growth of semiconductor nanocrystals was investigated by using Raman spectroscopic and imaging methods. The method was further extended to other graphene-based materials, which are easily prepared in a larger scale, such as exfoliated graphite oxide (EGO).