In this work, the influence of carbon nanofiber on the performance of TiO2-modified activated carbon (TiO2-AC) as photocatalyst for advanced water treatment was studied. TiO2-modified carbon nanofiber/activated carbon in powder form (TiO2-CNF/PAC) and in granular form (TiO2-CNF/GAC) were prepared by sol-gel method. Comparative morphological characterization studies for TiO2-CNF/PAC and TiO2-CNF/GAC and their testing for 25 mgL1 humic acid (HA) degradation showed a better performance of the overall sorption-involved photocatalysis using TiO2-CNF/GAC

Lazau, Carmen

Manea, Florica

Orha, Corina

Ursu, Daniel

Orha Corina

Lazau Carmen

Manea Florica

Ursu Daniel

University of Szeged

23rd International Symposium on Analytical and Environmental Problems 244   EFFECT OF CARBON NANOFIBER ONTO TiO2-MODIFIED POWDER/GRANULAR ACTIVATED CARBON FOR ADVANCED WATER TREATMENT  Corina Orha1, Carmen Lazau1, Florica Manea2*, Daniel Ursu1  1National Institute for Research and Development in Electrochemistry and Condensed Matter, no 144 A. Paunescu Podeanu Street, Timisoara 300569   2“Politehnica” University of Timisoara, P-ta Victoriei, No. 2, Timisoara e-mail: florica.manea@upt.ro  Abstract In this work, the influence of carbon nanofiber on the performance of TiO2-modified activated carbon (TiO2-AC) as photocatalyst for advanced water treatment was studied. TiO2-modified carbon nanofiber/activated carbon in powder form (TiO2-CNF/PAC) and in granular form (TiO2-CNF/GAC) were prepared by sol-gel method. Comparative morphological characterization studies for TiO2-CNF/PAC and TiO2-CNF/GAC and their testing for 25 mgL-1 humic acid (HA) degradation showed a better performance of the overall sorption-involved photocatalysis using TiO2-CNF/GAC.   Introduction Natural organic matters presence in drinking water source is responsible for membrane fouling in ultra- or nano-filtration steps of the advanced drinking water treatment technology. For this reason, various approaches have been investigated for the development of cheaper and more effective materials characterized by advanced properties suitable for the adsorption and photocatalysis applications in the water treatment.  Photocatalysis, one of the advanced water treatment processes, has been extensively studied to eliminate natural pollutants from water in the presence of semiconductor catalyst and UV illumination [1]. It is obviously that semiconductor catalyst is responsible for photocatalysis performance and among various materials used as semiconductors, titanium dioxide (TiO2) has been widely used for a broad range of applications because it is cheap, non-toxic, very active and stable in chemical reactions [2-4]. Various carbonaceous materials, e.g., activated carbon (AC), carbon nanotubes and carbon nanofibers (CNFs) have been intensively tested as sorbents, composite filters, antifouling membranes and support for photocatalysis processes. Composite materials based on titanium dioxide and activated carbon are receiving increasing attention for the degradation of humic, phenolic compounds, pesticides, chlorinated compounds and dyes because the activated carbon possesses high surface area, suitable pore structure and as consequence, high adsorption capacity and nano-sized TiO2 facilitates photocatalysis [5-7]. However, the size of activated carbon influences the sorption charactersitics and its combination with a nanostructured carbon should improve its performance. The aim of this paper is to explore the role of CNF as support for TiO2 in conjunction with powder and granular activated carbon, in form of TiO2-CNF/GAC and TiO2-CNF/PAC synthesized by sol-gel method and tested for the removal and the degradation of  humic acid, the main constituent of natural organic matters from water.     23rd International Symposium on Analytical and Environmental Problems 245   Experimental All the chemicals were of analytical purity grade and used as received. Composite materials based on titanium dioxide-modified carbon nanofiber and activated carbon were prepared using 5 mL titanium tetraisopropoxide with a purity of 97 % (TTIP, Aldrich) as titanium precursor, 2 g of powder/granular activated carbon (Flochem Industries) and 1 g carbon nanofiber (Nanocyl, Belgium) as matrix. The mixture was vigorously magnetic stirring (700 rpm, IKA RCT basic stirrer) in the presence of 30 ml ethanol and 30 ml distilled water, and pH solution value of 2 was adjusted with HNO3. After three hours of continuous stirring the composite materials were filtered, washed, and dried at 60ºC for 4 hours. The thermal treatment was realized at 400ºC for 3 hours. The morphology of the TiO2-CNF/PAC and TiO2-CNF/GAC composites was studied by a scanning electronic microscope (SEM, Inspect S PANalytical Model) coupled with the energy dispersive X-Ray analysis detector (EDX). The photocatalytic experiments were carried out under magnetic stirring at 20°C into a RS-1 photocatalytic reactor (Heraeus, Germany), which consisted of a submerged UV lamp surrounded by a quartz shield.  For each experiment, an adsorption step of 30 minutes was assured under the same hydrodynamic conditions without UV irradiation.  At certain running time, the suspension was sampled and filtered through a 0.4 µm membrane filter. The concentration of humic acid was measured in terms of absorbance at 254 nm (A254) using a Carry 100 Varian spectrophotometer. The HA removal efficiency was calculated using the following equation: Removal efficiency = 10000 ccc t   (%)        (1) where:  C0 and Ct are the concentrations of HA in aqueous solution in term of A254 at initial time and at any time t, respectively (mgL-1).   Results and discussion Figure 1 a-d presents SEM images for TiO2-PAC,  TiO2-GAC,  TiO2-CNF/PAC and TiO2-CNF/GAC. From SEM images, it is clearly seen that PAC and GAC have a layered structure, CNF have covered complete and uniform the both forms of activated carbon, forming a mesh on which TiO2 nanoparticles characterized by spherically shape are distrubuted more uniform in comparison with PAC and GAC modified with TiO2.     23rd International Symposium on Analytical and Environmental Problems 246    a)  b)   c)  d) Fig.1. SEM/EDX images for a) TiO2-PAC,  b) TiO2-GAC, c) TiO2-CNF/PAC and d) TiO2-CNF/GAC  The performance of the TiO2 modified powdered activated carbon is tested for HA removal and degradation by the sorption and the photocatalysis process, with the mention that the sorption was considered as a prerequisite step of the photocatalysis process. The role of CNF in the composition of TiO2 modified activated carbon was checked  for the performance of the photocatalysis process. Figures 2 and 3 show the results of the photocatalysis involving sorption step applied for HA removal and degradation expressed as the HA removal efficiency, using TiO2-CNF/PAC and TiO2-CNF/GAC in comparison with TiO2-PAC and TiO2-GAC,  respectively. It can be noticed that the presence of CNF as support for TiO2 improved the sorption performance for TiO2-GAC while no effect on the TiO2-PAC is found.  Also, the overall performace of the sorption step-involved photocatalysis was better in the presence of CNF. A slight enhancement of TiO2-PAC performance was found by introduction of CNF as support for TiO2 that showed no necessity of CNF integration into TiO2-PAC composition for the  degradation of 25 mgL-1HA.   23rd International Symposium on Analytical and Environmental Problems 247     Fig. 2. Evolution of HA removal (25mgL-1) efficiency versus time by sorption step-involved photocatalysis under UV irradiation using a)TiO2-CNF/PAC and b) TiO2-PAC Fig.3. Evolution of HA removal (25mgL-1) efficiency versus time by sorption step-involved photocatalysis under UV irradiation using a)TiO2-CNF/GAC and b) TiO2-GAC Due to the overall photocatalysis contains sorption and photocatalysis component, an assessment of the photocatalysis component was done by subtracting sorption component from the overall performance and the comparative results are presented in Figure 4. It can be noticed that the highest performance of photocatalysis was obtained for TiO2-GAC composite with the mention that these materials were tested only for 25 mgL-1 HA and the overall photocalaysis performance was higher than 90%, which imposes further studies for higher HA concentrations.    Fig. 4. Evolution of HA removal (25mgL-1) efficiency versus time by photocatalysis under UV irradiation using a) TiO2 –GAC; b) TiO2 –CNF/GAC; c)TiO2 – CNF/PAC and d) TiO2 –PAC  A very important aspect is the stability of the material and their morphologies were tested also, after the photocatalysis application. The SEM images of  TiO2–CNF/PAC and TiO2–CNF/GAC are gathered in Figure 5a and b, and it can be noticed the presence of TiO2 and CNF into catalyst composition, which denotes their good stability.  23rd International Symposium on Analytical and Environmental Problems 248   a) b) Fig.5. SEM/EDX images recorded after phototcalysis application of  a) TiO2-PAC,  b) TiO2-GAC  Conclusion TiO2-CNF/PAC and TiO2-CNF/GAC composite materials were successfully synthesized by sol-gel method. CNF covered activated carbon forming a mesh layer that assured a better and more uniform distribution of TiO2 onto carbanaceous support. TiO2-CNF/PAC, TiO2-CNF/GAC, TiO2-PAC and TiO2-GAC acted as photocatalyst towards humic acid degradation and allowed the removal of 25 mgL-1 HA with an overall photocatalysis performance higher than 90%.  The presence of CNF into composite allowed a slight enhancement of sorption properties of granular activated carbon without any effect onto the powdered activated carbon for removal of 25 mgL-1 HA. The morphology characterization of the composite after their application in the photocatalysis proved a good stability of the material that reclaim their potential for the further studies, which will envisage more concentrated humic acid removal from water.  Acknowledgements This work was supported by the Romanian National Research Programs PN 16 14 02 02 and PN-III-P2-2.1-PED-2016, 69PED/2017.  References [1] M. H. Baek, J. W. Yoon, J. S. Hong, J. K. Suh, Applied Catalysis A: General 450 (2013) 222. [2] S. Helali, E. Puzenat, N. Perol, M.J. Safi, C. Guillard, Appl. Catal. A: Gen. 402 (2011) 201.  [3] Y. Li, L. Li, C. Li, W. Chen, M. Zeng, Appl. Catal. A: Gen. 427 (2012) 1. [4] A. A. Vega, G.E. Imoberdorf, M. Mohseni, Appl. Catal. A: Gen. 405 (2011) 120. [5] M. Munner, M. Qamar, M.Saquib, D.W.Bahnemann, Chemosphere 61 (2005) 457.  [6] S. Liu, M. Lim, R. Fabris, C. Chow, K. Chiang, M. Drikas, R. Amal, Chemosphere 72, (2008) 263.  [7] X.Wang, Y.Liu, Z.Hu, Y.Chen, W.Liu, G. Zhao, J. Hazard. Mater., 169,  (2009) 1061.      

Effect of carbon nanofiber onto TiO2-modified powder/granular activated carbon for advanced water treatment

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Effect of carbon nanofiber onto TiO2-modified powder/granular activated carbon for advanced water treatment

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