An electrocatalytic active hybrid material prepared by successive stepwise coordinative deposition of 20 nm diameter gold nanoparticles (AuNP) with 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (TPyP) on fluorine-doped tin oxide (FTO) substrates previously modified with 3-mercaptopropylsilane is described. Their interaction and assembly were studied by UV-Vis spectroscopy and surface enhanced Raman spectroscopy to understand the kinetics as well as the conformation on the porphyrin macrocycle on the electrode surface as a function of its concentration. The hybrid nanomaterial was a build-up in reproducible successive deposition steps as confirmed by the linear rise of the absorption bands assigned to AuNP and TPyP as a function of the number of AuNP/porphyrin hybrid deposition steps, as supported by scanning electron microscopy (SEM) images. Electrodes modified with the hybrid nanomaterials were prepared and characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), as well as their electrocatalytic properties for the oxidation of nitrite and sulfite investigated. FTO electrodes modified with the AuNP/TPyP hybrid showed remarkable electrocatalytic activity as confirmed by reproducible and sensitive amperometric responses for sensing nitrite and sulfite in comparison to the bare electrode while reducing overpotentials respectively to 0.8 and 0.4 V and improving the dynamic range (linear response allowing quantification in the 50 to 500 µmol L-1 range) for detection of analytes.

Sugarcane waste ash, a Si-rich waste product, is generated in large quantities and creates a serious disposal problem in the Brazilian ethanol-sugar industry, affecting the environment and public health. Here, a simple method capable of generating bare silica nanoparticles utilizing this residue is demonstrated. Firstly, the crystalline silica present in sugarcane waste ash (SWA) was converted into amorphous by melting a mixture of sodium hydroxide and SWA at 550 ºC for 1 h. The silica nanoparticles (SiO2NPs) were formed by lowing pH. This production process of SiO2NPs from SWA was optimized varying the ash:NaOH mass ratio, increasing the silica extraction up to 96%. The sample’s composition was characterized by total X-ray fluorescence spectroscopy, morphology and physical-chemical properties were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction, specific surface area measurements, Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analyses (TGA), followed by use as adsorbent for the removal of methylene blue dye. With this process of extraction, nanoparticles smaller than 100 nm were generated, with a surface area of 63 m2 g-1 and a maximum adsorption capacity of 37 mg g-1 for methylene blue. The results indicate a successful process for obtaining an adsorbent from an industrial waste product using a cost effective and rapid synthesis procedure rendering renewable product.