Telah dilakukan sintesis silika gel dari bahan dasar abu sekam padi (ASP) dengan metode sol-gel. Silika gel yang diperoleh diaplikasikan untuk mempelajari adsorpsi zat warna direct red 12B (DR 12B). Sintesis silika gel dilakukan dengan menambahkan larutan H2SO4 4 M ke dalam larutan ASP yang mengandung natrium silikat. Larutan diperoleh dari melarutkan ASP dengan NaOH 2 M pada 500 °C selama 30 menit. Silika gel yang dihasilkan dikarakterisasi dengan difraktometer sinar-X (XRD), spektrofotometer inframerah (FTIR) dan penentuan kadar air. Adsorpsi zat warna DR 12B pada silika gel dilakukan dengan mempelajari pengaruh konsentrasi zat warna, waktu kontak, massa adsorben dan pengaruh pH pada jumlah zat warna yang teradsorpsi. DR 12B yang teradsorpsi secara kuantitatif dihitung dari selisih konsentrasi DR 12B dalam larutan sebelum dan sesudah adsorpsi berdasarkan analisis dengan spektrofotometer UV-VIS. Karakter dan kemampuan adsorpsi silika gel hasil sintesis dibandingkan dengan silika gel komersial (Kieselgel 60). Data adsorpsi digunakan untuk dasar dalam menentukan kapasitas dan energi adsorpsi menggunakan model isoterm Langmuir. Berdasarkan karakterisasi dengan XRD diperoleh bahwa silika gel berstruktur amorf. Data spektra IR menunjukkan bahwa silika gel hasil sintesis memiliki serapan spesifik untuk gugus-gugus fungsional seperti silanol (Si-OH) dan siloksan (Si-O-Si). Kadar H2O dari silika gel hasil sintesis (1,111 mmol/g) lebih rendah dibandingkan dengan silika gel Kieselgel 60 (3,749 mmol/g). Kapasitas adsorpsi DR 12B pada silika gel sintetik (0,310 mmol/g) lebih rendah daripada silika gel Kieselgel 60 (0,515 mmol/g). Energi adsorpsi pada silika gel sintetik dan silika gel Kieselgel 60 tidak jauh berbeda yaitu 21,610 kJ/mol dan 22,488 kJ/mol, yang mengindikasikan interaksi masing-masing melalui kemisorpsi. Pengaruh pH terhadap adsorpsi menunjukkan bahwa kemampuan adsorpsi baik silika gel maupun silika gel Kieselgel 60 menurun seiring bertambahnya pH.

Synthesis of silica gel from rice hull ash (ASP) by sol-gel process has been carried out. Silica gel was then used for studying adsorption of direct red 12B (DR 12B). Synthesis of silica gel was done by adding H2SO4 4 M to the ASP solution which the main component is natrium silicate. The solution was obtained from destruction of ASP with NaOH 2 M at 500 ºC for 30 minutes. Silica gel produced was characterized by X-ray diffractometer (XRD), infrared spectrophotometer (FTIR) and by determination of its silanol groups. The adsorption of DR 12B on silica gel was studied by evaluating the effect of DR 12B concentration, contact time, adsorbent mass and pH on the amount of DR 12B adsorbed. DR 12B adsorbed was calculated based on difference between DR 12B concentration before and after adsorption which was analysed using UV-VIS spectrophotometer. Characters and ability of synthesized silica gel in adsorbing DR 12B were compared to those of commercial silica gel (Kieselgel 60). Adsorption data was used for calculating capacity and energy of adsorption using Langmuir isotherm model. Based on characterization with XRD, silica gel is amorphous structure. Spectra of IR shows that synthesized silica gel has specific groups of silanol (Si- OH) and siloxane (Si-O-Si). Content of H2O in synthesized silica gel (1.111 mmol/g) is lower than that in commercial silica gel Kieselgel 60 (3.749 mmol/g). The adsorption capacity of DR 12B on synthetic silica gel (0.310 mmol/g) is lower than that on Kieselgel silica gel 60 (0.515 mmol/g). Adsorption energy on synthetic silica gel and on Kieselgel silica gel 60 is almost similar (21.610 kJ/mol and 22.488 kJ/mol, respectively), indicating that interaction occurred through chemisorption. The study of effect of pH on the adsorption shows that in the investigated pH range (2-10), capability of adsorption is decreased with increasing the pH value.

Kata Kunci : Abu sekam padi,Adsorpsi,Silika gel,Silika gel kieselgel 60,DR 12B, rice hull ash, adsorption, silica gel, Kieselgel silica gel 60, DR 12B