Polymer Communication Comments on “Chitosan functionalized with 2[-bis-(pyridylmethyl) aminomethyl]4-methyl-6-formyl-phenol: equilibrium and kinetics of copper (II) adsorption” Yuh-Shan Ho * School of Public Health, Taipei Medical University, 250 Wu-Hsing Street, Taipei 11014, Taiwan, ROC Received 8 September 2004; received in revised form 11 November 2004; accepted 12 November 2004 Available online 7 January 2005 Keywords: Adsorption; Kinetics; Pseudo-second-order Recently, Justi et al. [1] published the paper entitled as above. In Section 3.3. Adsorption kinetics, the authors mentioned a pseudo-second-order equation in the paper and cited a paper as secondary reference [2]. In the reference [2], the authors cited two papers published by Ho and McKay [3,4] for pseudo-second-order rate equation expression. Indeed, Ho developed a second-order kinetic expression for the sorption systems of divalent metal ions using sphagnum moss peat [5]. To distinguish the kinetic equation based on the adsorption capacity of a solid from the concentration of the solution, the second-order rate expression has been named pseudo-second-order [1–15]. The earlier application of the pseudo-second-order equation to the kinetic studies of competitive heavy- metal adsorption by sphagnum moss peat was undertaken by Ho et al. [6]. A modified pseudo-second-order kinetic expression was reported in 1998 [3,7], and has also been presented in the following years [4,9]. In addition, Azizian presented a theoretical analysis of pseudo-second-order equations [8]. The most frequently cited pseudo-second- order kinetic expression papers were published in Environ- mental Technology [6], Chemical Engineering Journal [7], Process Biochemistry [9], and Water Research [4]. More- over, similar comments have also been published in Bioresource Technology [10], Environmental Science and Technology [11], Journal of Colloid and Interface Science [12], Journal of Hazardous Materials [13], Water Research [14], and Industrial and Engineering Chemistry Research [15]. The pseudo-second-order rate expression of Ho has been widely applied to the sorption of metal ions, dyes, herbicides, oil and organic substances from aqueous solutions [10–14]. Research papers contribute not only by its originality and creativity, but also by its continuity and development toward subsequent research. Readers of published scientific articles may wish to retrieve cited references to further their follow-up researches and knowledge or to confirm claims made by the researchers [16]. However a reference section can play a key role for researchers who are interested in the paper’s statement and would like to follow the study or find useful information from the paper [17]. I suggest that Justi et al. cite Ho’s original pseudo-second-order kinetic expression paper. References [1] Justi KC, Laranjeira MCM, Neves A, Mangrich AS, Fa ´vere VT. Chitosan functionalized with 2[-bis-(pyridylmethyl) aminomethyl]4- methyl-6-formyl-phenol: equilibrium and kinetics of copper(II) adsorption. Polymer 2004;45(18):6285–90. [2] Wu FC, Tseng RL, Juang RS. Kinetic modeling of liquid-phase adsorption of reactive dyes and metal ions on chitosan. Water Res 2001;35(3):613–8. [3] Ho YS, McKay G. A comparison of chemisorption kinetic models applied to pollutant removal on various sorbents. Process Safety Environ Protect 1998;76(B4):332–40. [4] Ho YS, McKay G. The kinetics of sorption of divalent metal ions onto sphagnum moss peat. Water Res 2000;34(3):735–42. 0032-3861/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2004.11.109 Polymer 46 (2005) 1451–1452 www.elsevier.com/locate/polymer * Tel.: C886 2 2736 1661x6514; fax: C886 2 2738 4831. E-mail address: ysho@tmu.edu.tw.