Silver Doped TiO2 Nanoparticles: Preparation, Characterization and Efficient Degradation of 2,4-dichlorophenol Under Visible Light

Hydrothermally synthesized TiO2 nanoparticles containing different amounts of silver were characterized by X-Ray diffraction (XRD), Fourier transform infrared (FT-IR) and scanning electron microscopy equipped with energy dispersive X-ray microanalysis (SEM/EDX) techniques. XRD results showed prepared samples include 100% anatase phase. The presence of silver in TiO2 nanoparticle network was established by XRD, SEM/EDX and FT-IR techniques. The photocatalytic performance of the prepared catalysts was tested for the degradation of 2,4-dichlorophenol (2,4-DCP) under visible light.. The experiments demonstrated that 2,4-DCP was effectively degraded in the presence of Ag/TiO2 samples. It was confirmed that the presence of Ag on TiO2 catalysts could enhance the photocatalytic degradation of 2,4-DCP in aqueous suspension. It was found that an optimal dosage of 1.68 wt% Ag in TiO2 achieved the fastest 2,4-DCP degradation (95% after 180 min irradiation) under the experimental conditions. On the basis of various characterizations of the photocatalysts, the reactions involved to explain the photocatalytic activity enhancement due to Ag doping include a better separation of photogenerated charge carriers. GC-MS analysis showed the major intermediates of 2,4-DCP degradation are simple acids like oxalic acid, acetic acid, etc. as the final products

Separation of Reactive Red 120 Dye from Aqueous Solution by NiFe2O4-SiO2/PVDF Nanocomposite Membranes

The discharge of dye-containing wastes by the dye-consuming industry causes irreparable damage to the environment and humans. Nowadays, the use of membrane separation technology is a new and applicable technology in dyes separation. However, membranes used in water and wastewater treatment suffer from problems such as permeability-selectivity trade-off as well as short life due to fouling. Therefore, in this study, we tried to improve the hydrophilicity and antifouling properties of polyvinylidene fluoride (PVDF) membranes by adding NiFe2O4-SiO2 nanocomposite and improve its performance in reactive dye separation from aqueous solution. For this purpose, first NiFe2O4-SiO2 nanoparticles were prepared by sol-gel method and then pure and NiFe2O4-SiO2/PVDF nanocomposite membranes were fabricated by wet phase inversion method and their performance was evaluated. The synthesized nanoparticles were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) methods. Membranes morphology, surface roughness, hydrophilicity of the membrane surface, separation performance, pure water flux, porosity and pore radius were characterized by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), contact angle tests (CA), pure water flux test (PWF) and gravimetric methods, respectively. Aqueous solution containing 10-30 ppm reactive red 120 was used as test wastewater. The results of the contact angle analysis showed that by addition of 0.3 wt.% NiFe2O4-SiO2 nanoparticles to the polymer matrix, the membrane contact angle decreased from from 77.5° in the pure membrane to 51.7° in the nanocomposite membrane. It showed an increase in membrane hydrophilicity. AFM results showed that the surface roughness decreased as NiFe2O4-SiO2 content increased in PVDF matrix. It was also found that nanocomposite membrane containing 0.3 wt.% NiFe2O4-SiO2 nanoparticles has the best separation performance among the other fabricated membranes and this membrane can reject reactive red 120 dye from aqueous solution completely (99.5%)

Effect of chitosan as a functionalization agent on the performance and separation properties of polyimide/multi-walled carbon nanotubes mixed matrix flat sheet membranes

The effect of chitosan as a functionalization agent on the performance and separation properties of polyimide/multi-walled carbon nanotubes mixed matrix flat sheet membranes were investigated. Polyimide (PI)/raw multi-walled carbon nanotubes (r-MWCNTs) and polyimide (PI)/chitosan-functionalized multi-walled carbon nanotubes (C-f-MWCNTs) mixed matrix membranes were fabricated by phase inversion method. Raw and functionalized multi-walled carbon nanotubes were characterized by transmission electron microscope (TEM). The membrane samples were characterized by SEM, FESEM, DSC and gas permeation tests using He, CO2 and CH4 as test gases. TEM results and gas permeation test using He as test gas showed that r-MWCNTs were generally closed ended and after functionalization, well dispersed open ended chitosan-wrapped MWCNTs were obtained. Gas permeation results showed that addition of 1wt.% (solid base) C-f-MWCNTs into casting dope can increase the CO2 and CH4 permeabilities by 20.48 and 0.71Barrer, respectively. The increase in permeabilities of CO2, CH4 and He in this study can be attributed to the presence of high diffusivity tunnels in the MWCNTs within the polyimide matrix. It is interesting that the CO2/CH4 selectivity was also increased by 51.4% (from 10.9 to 16.5) by addition of C-f-MWCNTs. DSC and FESEM results also revealed a very good dispersion and adhesion of the C-f-MWCNTs in the polyimide matrix

A mathematical analysis of hollow fiber spinning : bore and dope velocity profiles in the air gap

Hollow fiber membranes are the most applicable form of membranes in laboratory and industrial scale with their large surface to volume ratios. Hollow fiber membranes usually are fabricated by dry-wet solution spinning, where a polymer solution is co-extruded through an annular region with a bore fluid and the nascent hollow fiber passes through an air gap and then enters a liquid coagulation bath. The spinneret dimension, dope and bore fluid flow rates, air gap length, bore fluid and dope compositions and their physical properties, coagulant composition and condition, shear stress within a spinneret, the ratio of dope to bore fluid volumetric flow rate, and the take-up-to-initial velocity ratio (draw ratio) are the primary factors that determine the final hollow fiber morphology and separation properties. All of the aforementioned parameters are not independent and some of them are functions of others. The objective of this paper is to elucidate the interdependence between some of the above parameters. For this purpose, dope and bore fluid axial velocity in the air gap was assumed as a function of the axial distance from the spinneret outlet, z, and radial velocity as a function of the radial distance from the center of the hollow fiber, r, and z. Dimensionless equations of motion and continuity were then simplified and solved simultaneously based on preceding assumptions. It was found from the analysis that the dimensionless axial velocity of dope was a function of the Reynolds number, Capillary number and Stokes number indicating that the axial velocity acceleration in the air gap is determined by viscous, capillary, and gravity force gradients. It was also concluded that the optimum value of the ratio of bore liquid flow rate to dope flow rate is equal to 0.8 of the ratio of the cross-sectional area of the bore fluid to that of the dope at the spinneret outlet

Effect of raw multi-wall carbon nanotubes on morphology and separation properties of polyimide membranes

Raw multi wall carbon nanotubes (r-MWCNTs) were embedded as fillers inside the polyimide (PI) matrix and PI/r-MWCNTs mixed matrix membranes were fabricated by the phase inversion method. The TEM images and permeation results using helium as test gas showed that r-MWCNTs were generally closed ended and acted as impermeable nano particles. Gas permeation tests using CO2 and CH4 showed that the addition of r-MWCNTs into the dope solution increased the CO2/CH4 separation factor while decreasing the carbon dioxide and methane permeances. When the r-MWCNTs content was increased from 0% to 6 wt.%, permeance of CO2 in the flat sheet mixed matrix membranes decreased from 9.15 GPU to 5.49 GPU and CO2/CH4 separation factor increased from 19.05 to 45.75. Identical to flat sheet mixed matrix membranes, the addition of 2 wt.% r-MWCNTs into a spinning dope increased the CO2/CH4 separation factor from 46.61 to 72.20. The glass transition temperature of the mixed matrix flat sheet membranes increased with an increase in the r-MWCNTs content. This implies a good segmental-level attachment between the two phases that forms a rigidified polymer region at the polymer/r-MWCNTs interface. FESEM images showed well dispersed r-MWCNTs in the polymer matrix at a loading of 2 wt% r-MWCNTs