Preparation of Environmentally Friendly Adsorbent Using Oil Palm Boiler Ash, Bentonite and Titanium Dioxide Nanocomposite Materials

Using the products derived from agricultural wastes as low-cost adsorbent materials to remove organic or inorganic contaminants would be ideal, as these materials are readily available in many countries. This study aimed to prepare environmentally friendly adsorbents made from nanocomposite OPBA / Bentonite / TiO 2 . The coprecipita-tion method was used in preparing OPBA, and CTAB surfactant was added in bentonite preparation. Meanwhile, the manufacture of TiO 2 was carried out using the sol-gel method. Characterization was done by XRD, FTIR, SEM, and BET. The adsorbent spectra did not show a significant shift in absorption where the O-H bonds were be coming weaker due to the presence of TiO 2 in the interlayer of bentonite. Another possibility is due to the influence of calcination and heating. The O-H groups of H 2 O are hydroxylated and dehydrated from within between layers. The formation of the composite OPBA/TiO 2 /Bentonite does not change the crystallinity of TiO 2 significantly. This proves that there is no decrease in photocatalyst activity after the addition of OPBA and bentonite. The morphology of the whole sample has a flake-like structure that has pores. The addition of OPBA into Bentonite/TiO 2 causes a decrease in the specific surface area of the sample.


INTRODUCTION
Heavy metal pollution in the environment is a severe problem. Heavy metals directly impact human life, as they accumulate in the food chain, even in low amounts. Some heavy metals were found to have polluted water and exceeded the limit dangerous to life. A nano-adsorbent is required to remediate heavy metals (Lubis et al., 2022). The adsorption technique is an effective water filtration technique, because it effectively removes various contaminants and heavy metals, making its use easy (Wang et al., 2010). Using by-products derived from agricultural wastes as low-cost adsorbent materials to remove organic or inorganic contaminants would be ideal, as these materials are readily available in many countries. Oil Palm Boiler Ash (OPBA) is biomass with silica (SiO 2 ) content that has the potential to be utilized (N. Bukit et al., 2019;. Palm ash from the combustion of palm kernel shells and fruit fibers contains the chemical element Silica, 48.5% (B.F. Bukit, Frida, Humaidi, & Sinuhaji, 2022b; B.F. Bukit, Frida, Humaidi, Sinuhaji, et al., 2022;. It is reported that 4 million tonnes of OPBA are produced annually, which is expected to increase due to the increasing global demand for palm oil (Abdul Khalil et al., 2011). Research shows that OPBA can be used as an effective adsorbent for Cr(III) (Chun et al., 2001) Several studies on OPBA as adsorbents include. Modifying raw OPBA into OPBA composite can increase the surface area of the adsorbent. The larger the surface area of the adsorbent, the greater the adsorption area is. OPBA composites have excellent potential to remove COD, ammonia nitrogen, nitrate, and phosphorus from wastewater. Its fast absorption and high adsorption capacity, coupled with its natural abundance in the environment, is a low-cost adsorbent that can be used in various wastewater treatment applications ( . The adsorption ability of natural bentonite is not realized to its full potential when no modification is made. Therefore, bentonite modification is required (Ginting et al., 2017). The ability of bentonite can be increased by the pillarization process and the calcination process. The intercalation of polycation and calcination produces a bentonite layer that is stable and constant at high temperatures. The polycation that can be used is Titanium Dioxide (TiO 2 ). TiO 2 has a large specific surface area that allows it to be combined with other materials without blocking the pores of these materials. Bentonite pillarization using Ti cations is expected to increase the basal distance and specific surface area In this study, the preparation of environmentally friendly adsorbents made from nanocomposite OPBA, Bentonite, and TiO 2 was carried out to adsorb heavy metals.

MATERIAL AND METHOD Material
The material used in the study include OPBA from PT. DPI (Dhajaja Putra Indonesia) Asahan District North Sumatra Indonesia, Bentonite, TiCl 4 , 6M HCL, NH 4 OH Merck Pro Analis.

Preparation of OPBA and bentonite nanoparticle
OPBA waste was dried and calcined at 500°C for 5 hours and then milled with a ball mill type Planetary Ball Mill for 10 hours with a rotation of 250 rpm filtered using a 200 mesh sieve. Then, it was mixed OPBA with 7 M HCl at 70°C for 4 hours. OPBA was mixed with NH 4 OH at 70°C for 4 hours and then neutralizing the pH(B. F. Bukit, Frida, Humaidi, Sinuhaji, et al., 2022). Meanwhile, bentonite was calcined for 5 hours at 700°C. Bentonite was milled with a ball mill for 10 hours with a rotation of 250 rpm. Then, 0.2 moles of CTAB were mixed with distilled water. Bentonite, CTAB, and distilled water were mixed at a temperature of 100°C for 4 hours (Frida, Rahmat, et al., 2022).

Preparation of TiO 2 nanoparticle
TiCl 4 was mixed with NH 4 OH at a temperature of 70°C and a stirring speed of ± 300 rpm. Then, 0.5 M solution (NH 4 ) 2 SO 4 was added. The result of the reaction was in the form of a gel, separated and washed with deionized water to remove chlorine ions. Then, the gel was dispersed into an ethanol solution to remove water and reduce agglomeration during the drying process. The resulting TiO 2 was then dried at 60°C for 48 hours.

Preparation of OPBA, Bentonite, and TiO 2 nanocomposite
The preparation of OPBA, Bentonite, and TiO 2 nanocomposite was done by mixing them with NaOH and stirring them for 5 hours using a stirrer, then washed with deionized water. Furthermore, it was placed in the furnace at a temperature of 500°C for 3 hours.

FTIR analysis of adsorbent
FTIR analysis was carried out to determine the changes in functional groups that occurred in the compound. The changes in functional groups experienced by the compound indicate a chemical interaction between Natural rubber and filler. This infrared spectrum is analyzed by observing the typical frequencies of the functional group of the sample FTIR spectra. The FTIR used is the Agilent Cary 630 FTIR. This flexible benchtop FTIR instrument offers high performance and exceptional ease of use in an ultra-compact design. The FTIR of the adsorbent is shown in Figure 1.
Broadband around 629 cm −1 may be due to vibration of Ti-O bonds on the titanium dioxide lattice. However, involvement of TiO 2 , particles in the absorption is difficult to evaluate in the low spectrum region as well, because this band overlaps with the vibrations of the clay skeleton (B.

XRD analysis of adsorbent
XRD characterization is useful for obtaining diffraction patterns and crystal structures. The XRD used is the Shimadzu 6100 type (40 kV, 30 mA) with a wavelength of Cu-Kα1 = 1.5405 = 0.15406 nm, with a rate of 2°/min at an angle range of 2Ө = 5-70°. The XRD of the adsorbent is shown in Fig 2. Measurement of diffraction with an x-ray diffractometer produces data in the form of a diffraction pattern consisting of measurement data for 2θ angles and peak intensity at related angles. Using the Match-Phase Identification from Powder Diffraction Data application and the COD (Crystallography Open Database) database, the compounds that match the peaks at an angle of 2θ can be identified, given the results of the analysis. Table 1 shows the results of the XRD adsorbent data.
Reflection on 2θ indicates the crystal phase contained in the OPBA/TiO 2 /Bentonite composite is anatase crystal phase. The result shows that the formation of the composite OPBA/TiO 2 /Bentonite does not change the crystallinity of TiO 2 significantly. This proves that there is no decrease in photocatalyst activity after the addition of OPBA and bentonite.

SEM analysis of adsorbent
Scanning Electron Microscope can provide the information about the surface topography of a specimen. SEM characterization was carried out using the SEM TM3030 model. The morphology of the nanocomposite is shown in Figure 3.
The whole sample has a flake-like structure that has pores. PH plays an essential role in the formation of the previously synthesized TiO 2 . On the basis of several studies, variations in surface charge depend on the pH used in the synthesis process. In addition, agglomeration occurs on some parts of the surface. The agglomeration that occurs makes the surface morphology found homogeneous in certain areas (Ibrahim & Sreekantan, 2011).

BET analysis of adsorbent
The surface area analysis used is the analysis with the Brunauer, Emmet and Teller (BET) method, conducted using Quantachrome Nova 4200e.  On the basis of the data in Table 2, it can be seen that the addition of OPBA into Bentonite/ TiO 2 causes a decrease in specific surface area. There are two factors which cause a decrease in area specific surface, the first caused by the sintering process OPBA particles on the surface external and internal montmorillonite. Sintering is merging particles at high temperature (calcination 500°C for 3 hours). The second factor is closure of interlayer by OPBA particles. A decrease in specific surface area after OPBA dispersion occurs because OPBA enters the existing pores or partially covers them. Bentonite/TiO 2 surface so that OPBA covers the open pores. A decrease in the specific surface area can also result in reduced the adsorption ability of the material, however OPBA/Bentonite/TiO 2 composites have semiconductor properties that may be more dominant than  the area reduction factor the surface, so that ability to degrade organic compounds will be higher. The average pore radius increased when the OPBA composition was 15 g. It can be seen that the pore size of the entire sample at the mesoporous region (

CONCLUSIONS
The adsorbent spectra did not show a significant shift in absorption where the O-H bonds were becoming weaker due to the presence of TiO 2 in the interlayer of bentonite. Another possibility is due to the influence of calcination and heating. The O-H groups of H 2 O are hydroxylated and dehydrated between layers. The formation of the composite OPBA/TiO 2 /Bentonite does not change the crystallinity of TiO 2 significantly. This proves that there is no decrease in photocatalyst activity after the addition of OPBA and bentonite. The morphology of the whole sample has a flake-like structure that has pores. The addition of OPBA into Bentonite/TiO 2 causes a decrease in the specific surface area of the sample.