Surface Modification of Nanoporous Anodic Alumina during Self-Catalytic Atomic Layer Deposition of Silicon Dioxide from (3-Aminopropyl)Triethoxysilane

Changes associated to atomic layer deposition (ALD) of SiO2 from 3-aminopropyl triethoxysilane (APTES) and O3, on a nanoporous alumina structure, obtained by two-step electrochemical anodization in oxalic acid electrolyte (Ox sample) are analysed. A reduction of 16% in pore size for the Ox sample, used as support, was determined by SEM analysis after its coverage by a SiO2 layer (Ox+SiO2 sample), independently of APTES or O3 modification (Ox+SiO2/APTES and Ox+SiO2/APTES/O3 samples). Chemical surface modification was determined by X-ray photoelectron spectroscopy (XPS) technique during the different stages of the ALD process, and differences induced at the surface level on the Ox nanoporous alumina substrate seem to affect interfacial effects of both samples when they are in contact with an electrolyte solution according to electrochemical impedance spectroscopy (EIS) measurements, or their refraction index as determined by spectroscopic ellipsometry (SE) technique. However, no substantial differences in properties related to the nanoporous structure of anodic alumina (photoluminescent (PL) character or geometrical parameters) were observed between Ox+SiO2/APTES and Ox+SiO2/APTES/O3 samples.

Nanoporous Alumina Membranes for Sugar Industry: An Investigation of Sintering Parameters Influence onUltrafiltration Performance

Ultrafiltration membranes offer a progressive and efficient means to filter out various process fluids. The prime factor influencing ultrafiltration to a great extent is the porosity of the membranes employed. Regarding membrane development, alumina membranes are extensively studied due to their uniform porosity and mechanical strength. The present research work is specifically aimed towards the investigation of nanoporous alumina membranes, as a function of sintering parameters, on ultrafiltration performance. Alumina membranes are fabricated by sintering at various temperatures ranging from 1200–1300 °C for different holding times between 5–15 h. The morphological analysis, conducted using Scanning electron microscopy (SEM), revealed a homogeneous distribution of pores throughout the surface and cross-section of the membranes developed. It was observed that an increase in the sintering temperature and time resulted in a gradual decrease in the average pore size. A sample with an optimal pore size of 73.65 nm achieved after sintering at 1250 °C for 15 h, was used for the evaluation of ultrafiltration performance. However, the best mechanical strength and highest stress-bearing ability were exhibited by the sample sintered at 1300 °C for 5 h, whereas the sample sintered at 1250 °C for 5 h displayed the highest strain in terms of compression. The selected alumina membrane sample demonstrated excellent performance in the ultrafiltration of sugarcane juice, compared to the other process liquids.

Influence of Pore-Size/Porosity on Ion Transport and Static BSA Fouling for TiO2-Covered Nanoporous Alumina Membranes

The influence of geometrical parameters (pore radii and porosity) on ion transport through two almost ideal nanoporous alumina membranes (NPAMs) coated with a thin TiO2 layer by the atomic layer deposition technique (Sf-NPAM/TiO2 and Ox-NPAM/TiO2 samples) was analyzed by membrane potential and electrochemical impedance spectroscopy measurements. The results showed the significant effect of pore radii (10 nm for Sf-NPAM/TiO2 and 13 nm for Ox-NPAM/TiO2) when compared with porosity (9% and 6%, respectively). Both electrochemical techniques were also used for estimation of protein (bovine serum albumin or BSA) static fouling, and the results seem to indicate deposition of a BSA layer on the Sf-NPAM/TiO2 fouled membrane surface but pore-wall deposition in the case of the fouled Ox-NPAM/TiO2 sample. Moreover, a typical and simple optical technique such as light transmission/reflection (wavelength ranging between 0 and 2000 nm) was also used for membrane analysis, showing only slight transmittance differences in the visible region when both clean membranes were compared. However, a rather significant transmittance reduction (~18%) was observed for the fouled Sf-NPAM/TiO2 sample compared to the fouled Ox-NPAM/TiO2 sample, and was associated with BSA deposition on the membrane surface, thus supporting the electrochemical analysis results.