Las nanopartículas sensibles a la luz como novela dibujan materiales solutos para el proceso de desalinización por ósmosis directa

Weldeabezgi, Tarik Hishe
Prof. Ivo Vankelecom (dir.) ; Dr. Yusak Hartanto (dir.)

Mallada, Reyes (ponente)

Universidad de Zaragoza, CIEN, 2019
Ingeniería Química y Tecnologías del Medio Ambiente department, Ingeniería Química area

Máster Universitario Erasmus Mundus en Ingeniería de Membranas

Abstract: Clean water shortage is one of the global major concerns. To overcome this problem, membrane-based desalination process, such as reverse osmosis (RO) have been developed in the recent years. However, this technology operates at a high hydraulic pressure to overcome the seawater osmotic pressure, making this desalination process still relatively expensive. Recently, forward osmosis (FO) process has become increasingly attractive over RO since it is capable to produce clean water by using natural osmotic pressure as the separation driving force provided by draw solution (DS), which eliminates the usage of high hydraulic pressure. DS is a critical material in the FO process, playing a key role in determining the separation performance and energy cost. After the FO process, DS requires a regeneration step to reconcentrate it to its initial state. As a result, the development of effective draw solution is essential for the advancement of FO technology.
In this master thesis work, the feasibility of light-responsive TiO2 nanoparticles was investigated as a draw solute in the FO process. Several dispersions of TiO2 nanoparticles in demineralized water (DI) with different concentration were prepared. These dispersions were tested for their FO performance with DI and saline water as feed solutions, respectively. The colloidal stability of TiO2 nanoparticles was achieved by deviation from the isoelectric point of the nanoparticles with a pH adjustment from 6 to 4.5.
The effects of TiO2 nanoparticle concentration, ultrasonication time, UV irradiation, primary particle size, and FO membrane orientation were tested using DI water as the feed solution. A concentration of 20 g / L of TiO2 was found as the optimum concentration for FO performance. The generated water flux was not linearly dependent on the nanoparticles concentrations but appeared to be dependent on how well the nanoparticles were dispersed. The effect of UV was investigated by testing the same amount of TiO2 with and without a UV treatment. The UV treated and sonicated before and after UV treatment generated a significantly higher water flux than the pristine one. The effect of the primary size of the nanoparticles was expressed in their response to UV radiation. In comparison to P5 (=5 nm), P15 (=15 nm), and P25 (= 25 nm), P5 showed the highest UV response. The effect of membrane orientation, namely pressure retarded osmosis (PRO) and forward osmosis (FO) mode were tested and the PRO mode resulted in a significantly higher water flux than FO mode due to its low concentration polarization effect, which consequently led to higher driving force than FO mode.
The TiO2 nanoparticles draw solutions were also characterized using DLS and FTIR to investigate the effect of UV on the particle size and hydrophilicity respectively. The DLS result showed a larger hydrodynamic diameter after UV treatment comparing to the pristine one but after ultrasonication, the hydrodynamic diameter was significantly decreased. This result confirmed that UV treatment promoted the agglomeration of nanoparticles. Longer UV irradiation time led to a moderately more hydrophilic surface than the shorter period as confirmed from the FTIR result.
The highest water flux generated with DI water feed solution by using the optimum concentration and parameters without any functionalization or capping agent was 15.8 LMH and this is quite promising.

Tipo de Trabajo Académico: Trabajo Fin de Master

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