The remaining synthesis solution is usually discarded after the nanoporous materials are collected. However, these conventional methods bring several drawbacks to the environment and industry. For instance, large amounts of initial reactants which remain unused in the remaining solution, including the expensive organic surfactant template, silica and corrosive solvent such as NaOH, is discarded

during the recovering of mesostructured particles. This causes the synthesis of nanoporous material an uneconomical process; it is not cost effective for chemical industries. Moreover, the disposal of unused chemical reagents especially the surfactant template after the synthesis results in severe health hazard and adverse check details environmental effect [10, 11]. Thus, any new insight regarding the replacing, recycling, or reusing of the valuable chemicals in the synthesis of nanoporous materials is highly appreciated. Recently, the use of electronic (e-waste)

[12] and natural wastes such as coal fly ash [13–17] and rice husk ash [18] as silica sources for the preparation of MCM-41 has been reported. In general, the ashes and electronic resin waste are treated with sodium hydroxide to extract the silica out before their introduction into the MCM-41 synthesis solution. With this strategy, the inorganic waste is re-used, and it can be converted into more valuable and useful PKC412 materials which may have important economic implications. In the environmental aspect, converting silica waste into nanoporous materials such as MCM-41 may provide another way for preserving the environment. Although

eco-friendly synthesis on MCM-41 using natural wastes has been reported to date, there is no study on the synthesis of MCM-41 by recycling the mother liquid. One of the reasons is that the change in the molar composition and the pH of the precursor solution will have a profound impact on the resulting materials, i.e., no solid product, amorphous, new or mixture of two mesophases aminophylline (lamellar, cubic, disordered) will be formed instead of the desired single hexagonal mesophase [2]. In this work, MCM-41 is prepared with a green synthesis strategy by reusing non-reacted reagents remaining in the synthesis solution followed by supplementary compensation of the consumed chemicals and pH adjustment. The chemical compositions of mother liquor and solid product of each cycle were then characterized by using dry solid mass analysis, thermogravimetry (TG)/differential thermal analysis (DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), 29Si magic-angle-spinning (MAS) solid-state nuclear magnetic resonance (NMR), transmission electron microscopy (TEM), atomic absorption spectrometry (AAS) and N2 adsorption-desorption analyses.