We report on the fabrication and opto-electronic characterization of solution-processed planar heterojunction perovskite solar cells based on methylammonium (MA) lead halide derivatives, MAPbI _3−x Y _x (Y = Cl, Br, I).

Heavy metal ions such as Cd²⁺, Pb²⁺, Cu²⁺, Mg²⁺, and Hg²⁺ from industrial waste water constitute a major cause of pollution for ground water sources. These ions are toxic to man and aquatic life as well, and should be removed from wastewater before disposal. Various treatment technologies have been reported to remediate the potential toxic elements from aqueous media such as adsorption, precipitation and coagulation. Most of these technologies are associated with some shortcomings, and challenges in terms of applicability, effectiveness and cost. However adsorption techniques have the capability of effectively removing heavy metals at very low concentration (1–100 mg/L). Various adsorbents have been reported in the literature for this purpose, including to a lesser extent, the use of hydrogel adsorbents for heavy metal removal in aqueous phase. Here, we provide an in depth perspective on the design, application and efficiency of hydrogel systems as adsorbents.

A Nafion-Graphene (Nafion-G) nanocomposite solution in combination with an in situ plated mercury film electrode was used as a highly sensitive electrochemical platform for the determination of Zn²⁺, Cd²⁺, Pb²⁺ and Cu²⁺ in 0.1 M acetate buffer (pH 4.6) by square-wave anodic stripping voltammetry (SWASV). Various operational parameters such as deposition potential, deposition time and electrode rotation speed were optimized. The Nafion-G nanocomposite sensing platform exhibited improved sensitivity for metal ion detection, in addition to well defined, reproducible and sharp stripping signals. The linear calibration curves ranged from 1 µg L⁻¹ to 7 µg L⁻¹ for individual analysis. The detection limits (3σ blank/slope) obtained were 0.07 µg L⁻¹ for Pb²⁺, Zn²⁺ and Cu²⁺ and 0.08 µg L⁻¹ for Cd²⁺ at a deposition time of 120 s. For practical applications recovery studies was done by spiking test samples with known concentrations and comparing the results with inductively coupled plasma mass spectrometry (ICP-MS) analyses. This was followed by real sample analysis.