Removing pollutants from water by using the photocatalyst TiO 2 is a highly-promising method. A large amount of work has been done to increase the activity of TiO 2 , whereas the main two findings are increasing the surface area and applying mixed phase modifications (anatase, brookite, and rutile). Here, we present a method to directly synthesize non-agglomerated TiO 2 nanoparticles with different crystal phase ratios via low temperature dissolution-precipitation (LTDRP) on a porous microfiltration membrane (polyethersulfone). The amount of hydrochloric acid and the temperature was varied between 0.1-1 M and 25-130 • C, respectively, while the concentration of titanium precursor (titanium(IV) isopropoxide) was kept unchanged. The TiO 2 nanoparticles and the membrane were thoroughly characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), measuring the water contact angle and permeation flux, and examining the degradation of methylene blue. The mixed phase anatase/brookite with a main component being anatase exhibited the highest photocatalytic activity in removing methylene blue. Higher synthesis temperature induces enhanced crystallinity and, subsequently, the degradation rate of methylene blue was improved. Additionally, the photocatalytic activity remains high and unchanged for up to nine repeated cycles, i.e., full recovery of the photocatalytic properties is sustained.
The occurrence of micropollutants in the environment is an emerging issue. Diclofenac, a non-steroidal anti-inflammatory drug, is one of the most frequently detected pharmaceuticals in the environment worldwide. Diclofenac is transformed by UVA light into different products with higher toxicity. The absorbance of the transformation products overlaps with the absorbance of diclofenac itself and inhibits the ongoing photoreaction. By adding polyvinylidene difluoride (PVDF), the products adsorb to the surface of PVDF. Therefore, phototransformation of diclofenac and total organic carbon (TOC) removal is enhanced and the toxicity decreased. At 15 min and 18 h of UVA treatment, removal of diclofenac and TOC increases from 56% to 65% and 18% to 54%, respectively, when PVDF is present. The toxicity of a UVA treated (18 h) diclofenac solution doubles (from 5 to 10, expressed in toxicity units, TU), while no toxicity was detectable when PVDF is present during UVA treatment (TU = 0). PVDF does not need to be irradiated itself but must be present during photoreaction. The adsorbent can be reused by washing with water or ethanol. Diclofenac (25 mg L−1) UVA light irradiation was monitored with high performance liquid chromatography (HPLC), UV-Vis spectroscopy and by analysing the decrease of TOC. The toxicity towards Vibrio fischeri was examined according to DIN EN ISO 11348-1: 2009-05. Density functional theory (DFT) was used to simulate the phototransformation products known in literature as well as further products identified via gas chromatography–mass spectrometry (GC-MS). The absorption spectra, reaction enthalpies (ΔH) and Gibbs free energy of reactions (ΔG) were calculated. The combination of UVA irradiation of diclofenac with adsorption of photoproducts to PVDF is unique and opens up new possibilities to enhance removal of pollutants from water.
Titanium dioxide (TiO 2 ) is described as an established material to remove pollutants from water. However, TiO 2 is still not applied on a large scale due to issues concerning, for example, the form of use or low photocatalytic activity. We present an easily upscalable method to synthesize high active TiO 2 nanoparticles on a polyethersulfone microfiltration membrane to remove pollutants in a continuous way. For this purpose, titanium(IV) isopropoxide was mixed with water and hydrochloric acid and treated up to 210 • C. After cooling, the membrane was simply dip-coated into the TiO 2 nanoparticle dispersion. Standard characterization was undertaken (i.e., X-ray powder diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, water permeance, contact angle). Degradation of carbamazepine and methylene blue was executed. By increasing synthesis temperature crystallinity and photocatalytic activity elevates. Both ultrasound modification of nanoparticles and membrane pre-modification with carboxyl groups led to fine distribution of nanoparticles. The ultrasound-treated nanoparticles gave the highest photocatalytic activity in degrading carbamazepine and showed no decrease in degradation after nine times of repetition. The TiO 2 nanoparticles were strongly bound to the membrane. Photocatalytic TiO 2 nanoparticles with high activity were synthesized. The innovative method enables a fast and easy nanoparticle production, which could enable the use in large-scale water cleaning.Catalysts 2018, 8, 376 2 of 16 efficiently from water. The main challenge is to generate a low cost, long-term stable, and reusable system with a high activity to degrade organic contaminants.The mode of application of TiO 2 is a crucial parameter as it already defines the degradation rate and success. Theoretically, the photocatalytic activity is the highest when using TiO 2 as nanoparticles in a suspension as the overall surface area can be immense. However, nanoparticles tend to agglomerate to larger particles (i.e., surface area is diminished) and after final cleaning the nanoparticles have to be removed extensively [9,10]. Binding TiO 2 to a support (e.g., membrane [11][12][13][14]) decreases the overall surface area but the degradation of pollutants can be executed in one step. Designing a porous support can overcome the surface area issues of a supported system. Membranes are ideal support systems as they are highly porous and can be produced easily, are cost effective, and exist in many different forms according to the need of the consumer. The pollutant is directly transported through the membrane to the photocatalyst for degradation. Slow transport of the pollutant to the photocatalyst (e.g., diffusion) is avoided. To generate a high surface area compound, the porosity should be high and the pore size low. Nonetheless, decreasing the pore size will increase the energy needed to operate the membrane system. Microfiltration membranes with a pore size of 0.22 and 0.45 µm have been successfully utilized [13,14].Other param...
Immobilization of proteins by covalent coupling to polymeric materials offers numerous excellent advantages for various applications, however, it is usually limited by coupling strategies, which are often too expensive or complex. In this study, an electron-beam-based process for covalent coupling of the model protein bovine serum albumin (BSA) onto polyvinylidene fluoride (PVDF) flat sheet membranes was investigated. Immobilization can be performed in a clean, fast, and continuous mode of operation without any additional chemicals involved. Using the Design of Experiments (DoE) approach, nine process factors were investigated for their influence on graft yield and homogeneity. The parameters could be reduced to only four highly significant factors: BSA concentration, impregnation method, impregnation time, and electron beam irradiation dose. Subsequently, optimization of the process was performed using the Response Surface Methodology (RSM). A one-step method was developed, resulting in a high BSA grafting yield of 955 mg m−2 and a relative standard deviation of 3.6%. High efficiency was demonstrated by reusing the impregnation solution five times consecutively without reducing the final BSA grafting yield. Comprehensive characterization was conducted by X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and measurements of zeta potential, contact angle and surface free energy, as well as filtration performance. In addition, mechanical properties and morphology were examined using mercury porosimetry, tensile testing, and scanning electron microscopy (SEM).
To increase the permeation performance and antifouling properties of polymer membranes, a one-step reaction using electron irradiation was developed. This process combines the surface activation of the membrane polymer and the simultaneous permanent immobilization of hydrophilic molecules. This technology can be applied to various polymers, flat sheet/hollow fiber membranes and all pore ranges. The roll-to-roll system developed for this enables all process steps including inline analysis for quality control of the membrane surface in a continuously operated system.
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