Understanding Graphene Response to Neutral and Charged Lead Species: Theory and Experiment

Abstract

Deep understanding of binding of toxic Lead (Pb) species on the surface of two-dimensional materials is a required prerequisite for the development of next-generation sensors that can provide fast and real-time detection of critically low concentrations. Here we report atomistic insights into the Lead behavior on epitaxial graphene (Gr) on silicon carbide substrates by thorough complementary study of voltammetry, electrical characterization, Raman spectroscopy, and Density Functional Theory (DFT). It is verified that the epitaxial graphene exhibits quasi-reversible anode reactions in aqueous solutions, providing a well-defined redox peak for Pb species and good linearity over a concentration range from 1 nM to 1 µM. The conductometric approach offers another way to investigate Lead adsorption, which is based on the formations of stable charge-transfer complexes affecting the p-type conductivity of epitaxial graphene. Our results suggest the adsorption ability of the epitaxial graphene towards divalent Lead ions is concentration-dependent and tends to saturate at higher concentrations. To elucidate the mechanisms responsible for Pb adsorption, we performed DFT calculations and estimated the solvent-mediated interaction between Lead species in different oxidative forms and graphene. Our results provide central information regarding the energetics and structure of Pb-graphene interacting complexes that underlay the adsorption mechanisms of neutral and divalent Lead species. Such a holistic understanding favors design and synthesis of new sensitive materials for water quality monitoring.

Electrochemical Deposition of Copper on Epitaxial Graphene

“…2.5 times at 0.5 V). This manifests the strong adsorption of di-cations on epitaxial graphene [77,78,93]. In parallel, the redox phenomena associated with the electrodeposition and dissolution of the metal species became explicit.…”

“…Exploiting epitaxial graphene grown on SiC (epitaxial graphene (EG)/SiC) using the hightemperature sublimation technique is regarded as an alternative strategy for sensing platform development. Due to evident advantages over other graphene family materials (namely, its large surface area free of functional groups, high quality of monolayer graphene, thickness uniformity, wide potential window, high signal-to-noise ratio, transfer-free technology, and direct sublimation growth without precursors [75][76][77]), epitaxial graphene has been tested with promising results for the real-time detection of Pb 2+ ions in aqueous solutions (with a detection limit far below the WHO's permissible level for lead in drinking water) through performing square-wave anodic stripping voltammetry and response-recovery measurements [78,79]. Inspired by this, we have recently extended our activities beyond lead detection to include the investigation of the electrochemical behavior of the Hg 2+ /Hg 0 redox couple at the epitaxial graphene working electrode [80]; now, we are aiming to elucidate the nature of the copper electroreduction at the epitaxial graphene surface.…”

Analisis Termodinamika Molekul Magnesium Sulphate (MgSO4)

“…Besarnya konduktivitas ini ditentukan oleh jumlah konsentrasi elektrolit. Energi listrik dapat ditransfer melalui materi berupa hantaran yang bermuatan listrik yang berwujud arus listrik yang berarti bahwa harus ada pembawa muatan listrik di dalam materi serta adanya gaya yang menggerakkan pembawa muatan tersebut (227)(228)(229)(230)(231) . Pembawa muatan dapat berupa elektron atau dapat juga digunakan ion positif dan ion negatif dalam larutan elektrolit dan leburan garam (232) .…”

SESIUM KLORIDA (CsCl) : TRANSPORT ION DALAM LARUTAN

“…Baik ion H + maupun ion Cd 2+ bergerak ke arah katoda, dengan ion H + bergerak lebih cepat. Antara larutan HCl (179-182) dan larutan CdCl2 terdapat perbatasan yang jelas, karena ion-ion Cd 2+ tidak mendahului ion-ion H + dan juga tidak ketinggalan di belakangnya karena larutan harus selalu netral (183)(184)(185)(186). (30) Kation bereaksi dengan percepatan menuju elektroda negative dan anion bereaksi dengan percepatan (241-245) menuju elektroda positif.…”