Mesoporous TiO2 Thin Films: State of the Art

Mesoporous TiO2 thin films (MTTFs), thanks to their particularly high surface area, controlled porosity, high flexibility in composition, and surface design, are promising candidates in different application fields such as sensors, self-cleaning coatings, lithium-ion batteries (LIBs), photocatalysis, and new-generation solar cells. This chapter is focused on the synthetic and post-synthesis aspects that can affect the TiO2 mesoporous structure and consequently the MTTF properties. In particular, after a brief summary of TiO2 properties, all experimental conditions to prepare MTTFs are reviewed as well as the main characterization techniques employed to study their physicochemical and photocatalytic properties. An overview of the main applications of MTTFs is also proposed, mainly focused on the use of MTTFs in sensors and LIBs

Pectinases immobilization on magnetic nanoparticles and their anti-fouling performance in a biocatalytic membrane reactor

Enzyme immobilization on commercial superparamagnetic nanoparticles (NPSP) was performed using covalent bonding. The biofunctionalized NPSP was then immobilized on the surface of the membrane using an external magnetic field to form a magneto-responsive biocatalytic membrane reactor (BMRSP). The magnetically formed smart nanolayer can be easily re-dispersed and recovered from the membrane when the enzyme is deactivated or whenever cleaning is required due to substrate over-accumulation. The system was used to hydrolyze pectin contained in different streams. Results are supported with complementary data from hydrodynamic, kinetic and morphological characterization in a flow-through reactive filtration. Wavelength-dispersive X-ray spectroscopy (WDS) elemental mapping revealed that the NPSP are uniformly dispersed on the surface of the membrane forming a thin biocatalytic layer. Both results of hydrodynamic studies and SEM micrographs of the membrane with the enzyme layer under various operating conditions, show that the immobilized enzyme effectively reduced membrane–foulant interaction. Comparison of filtration data using this commercial NPSP reveals good agreement with our previously used home-made NPSP. This implies that the scaling-up and commercialization of the developed BMRSP can be straightforward

Biorefinery of olive leaves to produce dry oleuropein aglycone:use of homemade ceramic capillary biocatalytic membranes in a multiphase system

Oleuropein aglycone is an important antioxidant compound produced during oleuropein hydrolysis, not yet commercially available. Its production from renewable material by green processes is a challenge because it permits waste re-use and low environmental impact. In this work, homemade asymmetric capillary ceramic membranes were used to develop biocatalytic membranes, which were further used to produce oleuropein aglycone from olive leaves and/or commercial oleuropein. Results indicated that the biocatalytic system (containing covalently immobilized β-glucosidase) promotes the hydrolysis of oleuropein in both monophase and multiphase processes. Furthermore, the multiphase biocatalytic system enables the extraction of the hydrophobic oleuropein aglycone in an organic phase, before its rearrangement in water. This was achieved by the production, of an unstable water-in-oil emulsion (permeate side), on the basis of membrane emulsification process. The intensified biocatalytic/extractor system allowed taking shelter the hydrophobic compound in the organic phase with good efficiency (90%), protecting it from rearrangement

Membrane Processes for Microplastic Removal

Plastic pollution of the aquatic environment is a major concern considering the disastrous impact on the environment and on human beings. The significant and continuous increase in the production of plastics causes an enormous amount of plastic waste on the land entering the aquatic environment. Furthermore, wastewater treatment plants (WWTPs) are reported as the main source of microplastic and nanoplastic in the effluents, since they are not properly designed for this purpose. The application of advanced wastewater treatment technologies is mandatory to avoid effluent contamination by plastics. A concrete solution can be represented by membrane technologies as tertiary treatment of effluents in integrated systems for wastewater treatment, in particular, for the plastic particles with a smaller size (< 100 nm). In this review, a survey of the membrane processes applied in the plastic removal is analyzed and critically discussed. From the literature analysis, it was found that the removal of microplastic by membrane technology is still insufficient, and without the use of specially designed approaches, with the exception of membrane bioreactors (MBRs)

Membrane Processes Based on Complexation Reactions of Pollutants as Sustainable Wastewater Treatments

Water is today considered to be a vital and limited resource due to industrial development and population growth. Developing appropriate water treatment techniques, to ensure a sustainable management, represents a key point in the worldwide strategies. By removing both organic and inorganic species using techniques based on coupling membrane processes and appropriate complexing agents to bind pollutants are very important alternatives to classical separation processes in water treatment. Supported Liquid Membrane (SLM) and Complexation Ultrafiltration (CP-UF) based processes meet the sustainability criteria because they require low amounts of energy compared to pressure driven membrane processes, low amounts of complexing agents and they allow recovery of water and some pollutants (e.g., metals). A more interesting process, on the application point of view, is the Stagnant Sandwich Liquid Membrane (SSwLM), introduced as SLM implementation. It has been studied in the separation of the drug gemfibrozil (GEM) and of copper(II) as organic and inorganic pollutants in water. Obtained results showed in both cases the higher efficiency of SSwLM with respect to the SLM system configuration. Indeed higher stability (335.5 vs. 23.5 hours for GEM; 182.7 vs. 49.2 for copper(II)) and higher fluxes (0.662 vs. 0.302 mmol·h-1·m-2 for GEM; 43.3 vs. 31.0 for copper(II)) were obtained by using the SSwLM. Concerning the CP-UF process, its feasibility was studied in the separation of metals from waters (e.g., from soil washing), giving particular attention to process sustainability such as water and polymer recycle, free metal and water recovery. The selectivity of the CP-UF process was also validated in the separate removal of copper(II) and nickel(II) both contained in synthetic and real aqueous effluents. Thus, complexation reactions involved in the SSwLM and the CP-UF processes play a key role to meet the sustainability criteria

Microencapsulation by Membrane Emulsification of Biophenols Recovered from Olive Mill Wastewaters

Biophenols are highly prized for their free radical scavenging and antioxidant activities. Olive mill wastewaters (OMWWs) are rich in biophenols. For this reason, there is a growing interest in the recovery and valorization of these compounds. Applications for the encapsulation have increased in the food industry as well as the pharmaceutical and cosmetic fields, among others. Advancements in micro-fabrication methods are needed to design new functional particles with target properties in terms of size, size distribution, and functional activity. This paper describes the use of the membrane emulsification method for the fine-tuning of microparticle production with biofunctional activity. In particular, in this pioneering work, membrane emulsification has been used as an advanced method for biophenols encapsulation. Catechol has been used as a biophenol model, while a biophenols mixture recovered from OMWWs were used as a real matrix. Water-in-oil emulsions with droplet sizes approximately 2.3 times the membrane pore diameter, a distribution span of 0.33, and high encapsulation efficiency (98% ± 1% and 92% ± 3%, for catechol and biophenols, respectively) were produced. The release of biophenols was also investigated

Preparation of Pd-Loaded Hierarchical FAU Membranes and Testing in Acetophenone Hydrogenation

Pd-loaded hierarchical FAU (Pd-FAU) membranes, containing an intrinsic secondary non-zeolitic (meso)porosity, were prepared and tested in the catalytic transfer hydrogenation of acetophenone (AP) to produce phenylethanol (PE), an industrially relevant product. The best operating conditions were preliminarily identified by testing different solvents and organic hydrogen donors in a batch hydrogenation process where micron-sized FAU seeds were employed as catalyst support. Water as solvent and formic acid as hydrogen source resulted to be the best choice in terms of conversion for the catalytic hydrogenation of AP, providing the basis for the design of a green and sustainable process. The best experimental conditions were selected and applied to the Pd-loaded FAU membrane finding enhanced catalytic performance such as a five-fold higher productivity than with the unsupported Pd-FAU crystals (11.0 vs. 2.2 mgproduct gcat−1·h−1). The catalytic performance of the membrane on the alumina support was also tested in a tangential flow system obtaining a productivity higher than that of the batch system (22.0 vs. 11.0 mgproduct gcat−1·h−1)

Benzene Hydroxylation and Simultaneous Extraction of Phenol in Two Membrane Contactors Made with Three-Compartment Cells

Two different three-compartment membrane contactors [called solid membrane contactor (SMC) and liquid membrane contactor (LMC)] were tested in the synthesis and separation of phenol produced by direct hydroxylation of benzene using a Fenton reaction. Phenol produced in the aqueous reacting phase was extracted in the organic phase and simultaneously stripped in the basic aqueous phase. Preliminary tests on phenol recovery evidenced better performances (86.5% of phenol recovered in the strip phase) using the SMC with 0.1 M Na₂SO₄ in the aqueous feed phase at 35 °C. In the tests of partial oxidation, higher phenol productivity (0.62 g_ph g_cat^–1 h^–1) was obtained in this last system because the high phenol flux away from the reacting phase permitted one to extract a high amount of phenol in the organic and aqueous (strip) phases. This extraction protected phenol by its subsequent oxidation. It was evidenced that the use of a third compartment containing an alkaline aqueous stripping phase permitted one to recover phenol at 100% purity