The adsorption of natural pigments onto TiO2 nanoparticles was investigated. The pigments were extracted from the dark purple colored pulp of the berry-like capsule of Kuduk-kuduk (Melastoma malabathricum L.). The Langmuir, Freundlich, Redlich-Peterson, and Sips isotherm models were used to analyze the equilibrium experimental data. Data correlated well with the Sips isotherm model, where the heterogeneity factor ( ) indicated heterogeneous adsorption characteristics, with a maximum adsorption capacity of 0.0130？mg/g. The heterogeneous adsorption character was further supported by results obtained from zeta-potential measurements. When a dye-sensitized solar cell (DSSC) was sensitized with the extracted pigment, the photo-energy conversion efficiency was measured to be 0.83%, thus proving the suitability of Kuduk-kuduk fruit pulp as a sensitizer in DSSCs. 1. Introduction Commercially, the quality of a product depends on the product value and acceptability. However, consumers are also attracted to the physical appearances of the product, especially to its colors. In food, beverages, and textile industries, the pigments are employed as coloring agents and for dyeing purposes. Natural colorants extracted from plants have been used for centuries before the first synthetic colorant was introduced. Low cost and ease of application have driven the drift from natural colorants to synthetic. However, due to environmental and health concerns associated with the applications of synthetic colorants the interest of using natural and organic sources as colorants has increased lately. Anthocyanins are natural, water-soluble, and nontoxic pigments which are responsible for the red, orange, pink, blue, or purple color of plants. The resultant color variation depends on the relative pH of the respective plant [1]. The anthocyanin pigments are expressed as red or pink under acidic media, purple in neutral media, and blue, green, or yellow in alkaline media. It turns colorless under extreme alkaline conditions [2]. Thus, anthocyanins also can be used as a pH indicator. Anthocyanins have been employed as additives or colorants in the food industry with limited usage due to its instability with varying pH levels [1]. In the alternative energy sector, natural dye extracts containing anthocyanins are integrated as sensitizers in dye-sensitized solar cells (DSSCs) because of their ability to absorb light [3, 4] and low cost associated with extraction procedures. Many researches had been conducted on analyzing the potential anthocyanins sensitizers extracted from natural
References
[1]
J. Li, X. D. Li, Y. Zhang et al., “Identification and thermal stability of purple-fleshed sweet potato anthocyanins in aqueous solutions with various pH values and fruit juices,” Food Chemistry, vol. 136, no. 3-4, pp. 1429–1434, 2013.
[2]
A. Andres-Bello, V. B. Palacios, P. Garcia-Segovia, J. Mir-Bel, and J. Martinez-Monzo, “Effect of pH on color and texture of food products,” Food Engineering Reviews, vol. 5, no. 3, pp. 158–170, 2013.
[3]
J. S. de Souza, L. O. M. de Andrada, and A. S. Polo, “Nanomaterials for solar energy conversion: dye-sensitized solar cells based on ruthenium (II) Tris-heteroleptic compounds or natural dyes,” in Nanoenergy, F. L. de Souza and E. R. Leite, Eds., pp. 49–80, Springer, Berlin, Germany, 2013.
[4]
M. R. Narayan, “Review: dye sensitized solar cells based on natural photosensitizers,” Renewable and Sustainable Energy Reviews, vol. 16, no. 1, pp. 208–215, 2012.
[5]
H. Zhou, L. Wu, Y. Gao, and T. Ma, “Dye-sensitized solar cells using 20 natural dyes as sensitizers,” Journal of Photochemistry and Photobiology A, vol. 219, no. 2-3, pp. 188–194, 2011.
[6]
M. Shahid, S. Ul-Islam, and F. Mohammad, “Recent advancements in natural dye applications: a review,” Journal of Cleaner Production, vol. 53, pp. 310–331, 2013.
[7]
G. Calogero, J.-H. Yum, A. Sinopoli, G. Di Marco, M. Gr？tzel, and M. K. Nazeeruddin, “Anthocyanins and betalains as light-harvesting pigments for dye-sensitized solar cells,” Solar Energy, vol. 86, no. 5, pp. 1563–1575, 2012.
[8]
S. M. Joffry, N. J. Yob, M. S. Rofiee et al., “Melastoma malabathricum (L.) smith ethnomedicinal uses, chemical constituents, and pharmacological properties: a review,” Evidence-Based Complementary and Alternative Medicine, vol. 2012, Article ID 258434, 48 pages, 2012.
[9]
N. T. R. N. Kumara, P. Ekanayake, A. Lim et al., “Layered co-sensitization for enhancement of conversion efficiency of natural dye sensitized solar cells,” Journal of Alloys and Compounds, vol. 581, pp. 186–191, 2013.
[10]
Q. Miao, M. Wu, W. Guo, and T. Ma, “Studies of high-efficient and low-cost dye-sensitized solar cells,” Frontiers of Optoelectronics in China, vol. 4, no. 1, pp. 103–107, 2011.
[11]
J. Lee, R. W. Durst, and R. E. Wrolstad, “Determination of total monomeric anthocyanin pigment content of fruit juices, beverages, natural colorants, and wines by the pH differential method: collaborative study,” Journal of AOAC International, vol. 88, no. 5, pp. 1269–1278, 2005.
[12]
Q. Sun and L. Yang, “The adsorption of basic dyes from aqueous solution on modified peat-resin particle,” Water Research, vol. 37, no. 7, pp. 1535–1544, 2003.
[13]
N. T. R. N. Kumara, P. Ekanayake, A. Lim, M. Iskandar, and L. C. Ming, “Study of the enhancement of cell performance of dye sensitized solar cells sensitized with Nephelium lappaceum (F: Sapindacea),” Journal of Solar Energy Engineering, vol. 135, no. 3, 5 pages, 2013.
[14]
N. T. R. Kumara, M. R. R. Kho, A. Lim et al., “DFT/TDDFT and experimental studies of natural pigments extracted from black tea waste for DSSC application,” International Journal of Photoenergy, vol. 2013, Article ID 109843, 8 pages, 2013.
[15]
K. Y. Foo and B. H. Hameed, “Insights into the modeling of adsorption isotherm systems,” Chemical Engineering Journal, vol. 156, no. 1, pp. 2–10, 2010.
[16]
N. M. Agyei, C. A. Strydom, and J. H. Potgieter, “An investigation of phosphate ion adsorption from aqueous solution by fly ash and slag,” Cement and Concrete Research, vol. 30, no. 5, pp. 823–826, 2000.
[17]
Y. S. Ho and G. Mckay, “Competitive sorption of copper and nickel ions from aqueous solution using peat,” Adsorption, vol. 5, no. 4, pp. 409–417, 1999.
[18]
S. Baup, C. Jaffre, D. Wolbert, and A. Laplanche, “Adsorption of pesticides onto granular activated carbon: determination of surface diffusivities using simple batch experiments,” Adsorption, vol. 6, no. 3, pp. 219–228, 2000.
[19]
A. Benhammou, A. Yaacoubi, L. Nibou, and B. Tanouti, “Adsorption of metal ions onto Moroccan stevensite: kinetic and isotherm studies,” Journal of Colloid and Interface Science, vol. 282, no. 2, pp. 320–326, 2005.
[20]
V. C. Srivastava, M. M. Swamy, I. D. Mall, B. Prasad, and I. M. Mishra, “Adsorptive removal of phenol by bagasse fly ash and activated carbon: equilibrium, kinetics and thermodynamics,” Colloids and Surfaces A, vol. 272, no. 1-2, pp. 89–104, 2006.
[21]
S. J. Allen, G. Mckay, and J. F. Porter, “Adsorption isotherm models for basic dye adsorption by peat in single and binary component systems,” Journal of Colloid and Interface Science, vol. 280, no. 2, pp. 322–333, 2004.
[22]
W.-T. Tsai, H.-C. Hsu, T.-Y. Su, K.-Y. Lin, and C.-M. Lin, “Adsorption characteristics of bisphenol-A in aqueous solutions onto hydrophobic zeolite,” Journal of Colloid and Interface Science, vol. 299, no. 2, pp. 513–519, 2006.
[23]
A. Artola, M. Martin, M. D. Balaguer, and M. Rigola, “Isotherm model analysis for the adsorption of Cd (II), Cu (II), Ni (II), and Zn (II) on anaerobically digested sludge,” Journal of Colloid and Interface Science, vol. 232, no. 1, pp. 64–70, 2000.
[24]
F.-C. Wu, B.-L. Liu, K.-T. Wu, and R.-L. Tseng, “A new linear form analysis of Redlich-Peterson isotherm equation for the adsorptions of dyes,” Chemical Engineering Journal, vol. 162, no. 1, pp. 21–27, 2010.
[25]
J.-P. Wang, H.-M. Feng, and H.-Q. Yu, “Analysis of adsorption characteristics of 2,4-dichlorophenol from aqueous solutions by activated carbon fiber,” Journal of Hazardous Materials, vol. 144, no. 1-2, pp. 200–207, 2007.
[26]
A. Tor and Y. Cengeloglu, “Removal of congo red from aqueous solution by adsorption onto acid activated red mud,” Journal of Hazardous Materials, vol. 138, no. 2, pp. 409–415, 2006.
[27]
S. Kundu and A. K. Gupta, “Adsorption characteristics of As(III) from aqueous solution on iron oxide coated cement (IOCC),” Journal of Hazardous Materials, vol. 142, no. 1-2, pp. 97–104, 2007.
[28]
A. ？zer and G. Dursun, “Removal of methylene blue from aqueous solution by dehydrated wheat bran carbon,” Journal of Hazardous Materials, vol. 146, no. 1-2, pp. 262–269, 2007.
[29]
M. Gr？tzel, “Solar energy conversion by dye-sensitized photovoltaic cells,” Inorganic Chemistry, vol. 44, no. 20, pp. 6841–6851, 2005.
