The effect of chemical modification of SiO2 nanoparticles on the nanofiltration characteristics of polyamide membrane

Removal of emerging organic micropollutants via modified-reverse osmosis/nanofiltration membranes: A review

Hazardous micropollutants (MPs) such as pharmaceutically active compounds (PhACs), pesticides and personal care products (PCPs) have emerged as a critical concern nowadays for acquiring clean and safe water resources. In the last few decades, innumerable water treatment methods involving biodegradation, adsorption and advanced oxidation process have been utilized for the removal of MPs. Of these methods, membrane technology has proven to be a promising technique for the removal of MPs due to its sustainability, high efficiency and cost-effectiveness. Herein, the aim of this article is to provide a comprehensive review regarding the MPs rejection mechanisms of reverse osmosis (RO) and nanofiltration (NF) membranes after incorporation of nanomaterials and also surface modification atop the PA layer. Size exclusion, adsorption and electrostatic charge interaction mechanisms play important roles in governing the MP removal rate. In addition, this review also discusses the state-of-the-art research on the surface modification of thin film composite (TFC) membrane and nanomaterials-incorporated thin film nanocomposite (TFN) membrane in enhancing MPs removal performance. It is hoped that this review can provide insights in modifying the physicochemical properties of NF and RO membranes to achieve better performance in water treatment process, particularly for the removal of emerging hazardous substances.

Modifying thin-film composite forward osmosis membranes using various SiO2 nanoparticles for aquaculture wastewater recovery

This paper describes the fabrication, modification, and evaluation of the performance of thin-film composite (TFC) forward osmosis (FO) membranes for lab-scale aquaculture wastewater recovery using various fumed silica (SiO₂) nanoparticles. The active polyamide (PA) layers of these membranes were novelly modified using different types of pretreated SiO₂ nanoparticles [virgin SiO₂, dried SiO₂, and 3-aminopropyltriethoxysilane (APTES)-modified SiO₂] and concentrations (0.05, 0,1, 0,2, and 0.4 wt%) to improve the membrane hydrophilicity with minimum particle agglomeration. Results show that the APTES-SiO₂ modified membrane had the highest water flux and selectivity, followed by the dried-SiO₂ modified membrane. The APTES coupling agent notably reduced the SiO₂ aggregation on the membrane surface and improved membrane hydrophilicity. Consequently, high permeate flux and an acceptable reverse solute flux were observed. The optimal SiO₂ concentration for PA modification was 0.1 wt% for all the nanoparticle types. The virgin and APTES-SiO₂ modified membranes were used for aquaculture wastewater recovery. The water recovery rate reached 47% in 84 h when using the APTES-SiO₂ modified membrane, while it reached only 26% in 108 h when using the virgin membrane. With a suitable design of the filtration apparatus and choice of draw solution (DS), the prepared novel TFC-FO membrane containing APTES-modified SiO₂ can be used for recycling aquaculture wastewater into the DS, which can then be reused for other purposes.

Cerium oxide doped nanocomposite membranes for reverse osmosis desalination

Cerium oxide (CeO₂) nanoparticles (NPs) have indicated great potentials as nanofiller owing to its high surface area, antioxidant properties and low cost. In this paper, thin film nanocomposite (TFN) RO membranes were proposed to be prepared through incorporation of hydrophilic CeO₂ NPs in polyamide (PA) selective layers via interfacial polymerization (IP). EDX, XPS, SEM, AFM, contact angle and zeta potential were used to examine the property and morphology of the prepared membranes. CeO₂ NPs were successfully embedded in the PA network, which endowed the TFN membranes with rougher surfaces and thinner PA layers. The TFN membranes were fabricated with different CeO₂ NPs contents (0, 50, 100, 150, 200, 400 mg/L). With increasing CeO₂ NPs loading amount, the hydrophilicity improved from 85.4° to 65.7° and the surface charge declined from -19.4 to -34.2 mV. These characteristics contributed to a 50% enhancement in water flux of TFN-CeO₂100 membrane (containing 100 mg/L of CeO₂ NPs) without compromise the NaCl rejection (98%). Moreover, CeO₂ embedded membrane exhibited an enhanced fouling resistance property through preventing the adhesion of hydrophobic foultants. This study demonstrated the desirable applicability of CeO₂ NPs in synthesizing novel TFN membranes for desalination application.

Important Approaches to Enhance Reverse Osmosis (RO) Thin Film Composite (TFC) Membranes Performance

Thin film composite (TFC) membrane, which consists of polyamide (PA) active film rests on porous support layer, has been the major type of reverse osmosis (RO) membrane since its development by Cadotte in the 1970s, and has been remarkably used to produce clean water for human consumption and domestic utilization. In the past 30 years, different approaches have been exploited to produce the TFC membrane with high water flux, excellent salt rejection, and better chlorine/fouling resistance. In this brief review, we classify the techniques that have been utilized to improve the RO-TFC membrane properties into four categories: (1) Using alternative monomers to prepare the active layer; (2) modification of membrane surface; (3) optimization of polymerization reactions; and (4) incorporation of nanoparticles (NPs) into the membrane PA layer. This review can provide insights to guide future research and further propel the RO TFN membrane.

Predicting the DNP-SENS efficiency in reactive heterogeneous catalysts from hydrophilicity

Identification of surfaces at the molecular level has benefited from progress in dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP SENS).

Identification of surfaces at the molecular level has benefited from progress in dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP SENS). However, the technique is limited when using highly sensitive heterogeneous catalysts due to secondary reaction of surface organometallic fragments (SOMFs) with stable radical polarization agents. Here, we observe that in non-porous silica nanoparticles (NPs) (d_particle = 15 nm) some DNP enhanced NMR or SENS characterizations are possible, depending on the metal-loading of the SOMF and the type of SOMF substituents (methyl, isobutyl, neopentyl). This unexpected observation suggests that aggregation of the nanoparticles occurs in non-polar solvents (such as ortho-dichlorobenzene) leading to (partial) protection of the SOMF inside the interparticle space, thereby preventing reaction with bulky polarization agents. We discover that the DNP SENS efficiency is correlated with the hydrophilicity of the SOMF/support, which depends on the carbon and SOMF concentration. Nitrogen sorption measurements to determine the BET constant (C_BET) were performed. This constant allows us to predict the aggregation of silica nanoparticles and consequently the efficiency of DNP SENS. Under optimal conditions, C_BET > 60, we found signal enhancement factors of up to 30.