Synthesis of nanosized ZSM-5 zeolite from rice straw using lignin as a template: Surface-modified zeolite with quaternary ammonium cation for removal of chromium from aqueous solution Ibraheem O. Ali, Mohamed S. Thabet, Karam S. El-Nasser, Ali M. Hassan, Tarek M. Salama ⇑ Department of Chemistry, Faculty of Science, Al-Azhar University, Nasr City, Cairo 11884, Egypt article info Article history: Received 3 January 2012 Received in revised form 16 April 2012 Accepted 18 April 2012 Available online 14 May 2012 Keywords: Rice straw Lignin Surfactant-modified ZSM-5 XRD Chromate removal abstract Extracted silica and lignin from local rice straw were respectively used as a source of silica and a templat- ing agent for the synthesis of nanosized ZSM-5 zeolite at different aging temperatures with the autoclave process. A comparative analysis between synthesized ZSM-5 with lignin (Z L ) and its respective synthe- sized with most common tetrapropyl-ammonium bromide (TPABr) (Z T ) using XRD, FT-IR, TEM, TGA/ DTGA and pore structure analysis by N 2 adsorption at 196 °C was conducted. A higher degree of crys- tallinity and a larger specific surface area (S BET ) were presented for Z L at aging temperature of 160 than at 140 °C. Concurrently, a decrease in intensity of the diffraction line at d = 3.342 Å A 0 due to a-quartz silica was seen, giving rise to an increase of the dissolution rate of silica component in the gel phase at 160 over 140 °C. Complementary TEM and XRD techniques informed that the particle sizes measured 50 and 75 nm for the former and latter, respectively. The Z L surface was modified with TPA + (50–200 mmol) and applied for chromate anions (5–30 ppm) adsorption experiments in the aqueous solution at room temperature and pH 5. The capacity of chromate adsorption over Z L -modified TPA + was greater by three- fold than over Z L by the combination of electrostatic effects. The kinetics obeyed Freundlich model where the adsorption onto Z L -modified TPA + affords 3.7 mmol/g. Ó 2012 Elsevier Inc. All rights reserved. 1. Introduction ZSM-5 is a medium pore zeolite formed by 5-membered rings which possesses a pore dimension of 0.54–0.56 nm. Its unique pore structure has excellent shape selectivity, while the ability to devel- op internal acidity makes it an interesting material for catalyzing organic reactions [1]. Since its discovery, extensive works have been carried out on the synthesis and applications of ZSM-5. High crystalline ZSM-5 can be synthesized within a period of about 168 h in autoclave at 120–180 °C under autogenous pressures. The autoclavation time can be reduced to 4–6 h under high pres- sures and temperatures (about 40–60 atm and 230–250 °C) [2–4]. Among the several common templates used for the synthesis of ZSM-5 is tetrapropyl ammonium bromide (TPABr), together with silica and alumina from pure chemical sources. Efforts have also been made to use rice husk (RHA) as a source of silica for the syn- thesis of ZSM-5 with the autoclave process [5–8]. RHA is a solid waste product from undesirable agricultural mass residue which is suitable for recycling. The amount of amorphous silica in the used rice husk is about 41% (w/w) while the ash from the unwashed husk contains about 96% (w/w) silica and some amount of organics, alkali oxide, and impurities. Rice straw ash can also be used as an alternative cheap source of amorphous silica for the production of silicon based materials with industrial and techno- logical interests [9,10]. In Egypt an enormous quantity of industrial waste grade of rice straw (RS) has been produced which directly affects upon the environment and imposes air pollution. To protect the environment and decrease the amount of RS waste products, it is essential to find an appropriate utilization of the ash. The silica in rice straw is amorphous and transforms to crystalline silica when it is heated at high temperatures. The transformation temperature is affected by its chemical purity and particle size. Industrial wastewater from textile, leather tanning, electroplat- ing, pigmentation and dyes contain chromium in high concentra- tion. Chromium exists in oxidation states from +2 to +6, but only two states, +3 and +6, are of environmental significance. Cr VI is more toxic and carcinogenic than Cr III because of its solubility in al- most the whole pH range and greater mobility than Cr III [11–13]. Cr VI forms several species, the relative proportions of which depend on both pH and total Cr VI concentration. Within the normal pH range in natural waters, Cr VI exists mainly as CrO 2 4 , HCrO  4 , and Cr 2 O 2 7 . As a guideline, World Health Organization (WHO) recom- mended a maximum level of 0.050 mg L 1 for Cr VI in drinking water and the National Institute for Occupational Safety and 1387-1811/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.micromeso.2012.04.020 ⇑ Corresponding author. Tel.: +20 2 22629357/8; fax: +20 2 22629356. E-mail address: tm_salama@yahoo.com (T.M. Salama). Microporous and Mesoporous Materials 160 (2012) 97–105 Contents lists available at SciVerse ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso