Solid-State Colorimetric Sensing and Removal of Cu(II) from Wastewater Samples using Chromoionophoric Probe Anchored Porous Polymer Monolith Templates

Abstract

Abstract

Copper toxicity causes adverse effects to mankind and other living organisms. Considering their industrial applications, it is an extreme necessity for their real-time monitoring in various water sources. At present, liquid based colorimetric sensing approaches are available for Cu(II) detection, but are associated with organic solvents for the dissolution of probe molecules, thus making it eco-unfriendly, besides causing water compatibility issues that affects the sensing performance in terms of kinetics, selectivity and sensitivity [1,4]. Therefore, we report a smart, simple, and fast approach using a bimodal meso-/macro-porous polymer monolithic support for the reliable solid-state optical sensing of ultra-trace concentrations of Cu(II) in industrial and environmental water samples. The solid-state opto-sensor is developed in a simple and easy procedure that involves direct immobilisation technique. The sensor construction is facilitated using a polymer monolith with multi-diffusible cage-like network that act as anchoring sites for the uniform dispersion/anchoring of the ion-receptor probe ligands i.e., 4-butyl-N-(2-(thiophene-2-carbonyl)hydrazine-1-carbonothioyl)benzamide (BTHCB) and 4-butyl-N-((1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)carbamothioyl)benzamide (BDICB). The BTHCB anchored polymer monolith (Sensor-I) enables a visual colour transition from colourless to greyish-black, and the BDICB anchored polymer monolith (Sensor-II) shows a colour transition from colourless to deep-green, with incremental addition of Cu(II), as shown in Scheme 1. The encapsulation of probes onto the high surface area polymer monolith material permits for the selective and sensitive naked-eye colorimetric detection of Cu(II). The structural and surface features of the polymeric sensors are characterized using FE-SEM, HR-TEM, EDAX, SAED, XPS, p-XRD, FT-IR and BET/BJH surface area/porosity analysis. The working performance of the sensor materials are optimized by analysing various experimental parameters namely solution pH, temperature, probe concentration, sensor quantity, kinetics, matrix interference, linear response range, etc. In wastewater, the sensors I & II show a lower detection limit of 0.14 & 0.11 ppb, along with a quantification limit of 0.56 & 1.0 ppb for Cu(II), respectively. The proposed solid-state optical sensors will be a viable industrial tool for the on-site real-time sensing and removal of Cu(II). The optical solid-state sensors possess numerous advantages in terms of quick response time under neutral pH condition, and are easily recoverable and reusable over 7 regenerative cycles. The proposed methodology shows that the synthesised probe (BTHCB) and (BDICB) molecules is more effective in captivating onto the designed polymer monolithic material and hence it bring forth to an excellent solid-state sensor system with no use of organic solvents, and re environmentally compatible for the ocular detection of ultra-trace Cu(II).