Syaifullah Muhammad

Different Crystallographic One-dimensional MnO2 Nanomaterials and Their Superior Performance in Catalytic Phenol Degradation

Three one-dimensional MnO2 nanoparticles with different crystallographic phases, α-, β-, and γ-MnO2, were synthesized, characterized, and tested in heterogeneous activation of Oxone for phenol degradation in aqueous solution. The α-, β-, and γ-MnO2 nanostructured materials presented in morphologies of nanowires, nanorods, and nanofibers, respectively. They showed varying activities in activation of Oxone to generate sulfate radicals for phenol degradation depending on surface area and crystalline structure. α-MnO2 nanowires exhibited the highest activity and could degrade phenol in 60 min at phenol concentrations ranging in 25-100 mg/L. It was found that phenol degradation on α-MnO2 followed first order kinetics with an activation energy of 21.9 kJ/mol. The operational parameters, such as MnO2 and Oxone loading, phenol concentration and temperature, were found to influence phenol degradation efficiency. It was also found that α-MnO2 exhibited high stability in recycled tests without losing activity, demonstrating itself to be a superior heterogeneous catalyst to the toxic Co3O4 and Co(2+).

A comparative study of spinel structured Mn3O4, Co3O4 and Fe3O4 nanoparticles in catalytic oxidation of phenolic contaminants in aqueous solutions

Spinel structured Mn3O4, Co3O4 and Fe3O4 nanoparticles were prepared, characterized, and tested in degradation of aqueous phenol in the presence of peroxymonosulfate. It was found that Mn3O4 and Co3O4 nanoparticles are highly effective in heterogeneous activation of peroxymonosulfate to produce sulfate radicals for phenol degradation. The activity shows an order of Mn3O4>Co3O4>Fe3O4. Mn3O4 could fast and completely remove phenol in about 20 min, at the conditions of 25 ppm phenol, 0.4 g/L catalyst, 2 g/L oxone®, and 25 °C. A pseudo first order model would fit to phenol degradation kinetics and activation energies on Mn3O4 and Co3O4 were obtained as 38.5 and 66.2 kJ/mol, respectively. In addition, Mn3O4 exhibited excellent catalytic stability in several runs, demonstrating that Mn3O4 is a promising catalyst alternative to toxic Co3O4 for water treatment.

Coal fly ash supported Co3O4 catalysts for phenol degradation using peroxymonosulfate

Several fly ash (FA) samples derived from Australian (FA-WA) and Brazilian coals (FA-JL and FA-CH) were used as supports to prepare Co oxide (Co)-based catalysts. These Co/FA catalysts were tested in peroxymonosulfate activation for sulphate radical generation and phenol degradation in aqueous solution. The physicochemical properties of FA supports and Co/FA catalysts were characterised by N2 adsorption, X-ray diffraction (XRD), scanning electron microscopy coupling with energy dispersive spectroscopy (SEM-EDS), elemental mapping, and UV-vis diffuse reflectance spectroscopy. It was found that the FA supports did not show adsorption of phenol and could not activate peroxymonosulfate for sulphate radical generation. However, fly ash supported Co oxide catalysts (Co/FA) presented higher activities in the activation of peroxymonosulfate for phenol degradation than bulk Co oxide and their activities varied depending on the properties of the fly ash supports. Co/FA-JL showed the highest activity while Co/FA-WA showed the lowest. Activation energies of phenol degradation on three Co/FA catalysts were obtained to be 47.0, 56.5, 56.0 kJ mol−1 for Co/FA-WA, Co/FA-JL and Co/FA-CH, respectively.

Activated carbons as green and effective catalysts for generation of reactive radicals in degradation of aqueous phenol

Several activated carbons (ACs) were used as metal-free catalysts for degradation of a toxic organic compound, phenol, in the presence of different oxidants, H2O2, peroxydisulfate (PS) and peroxymonosulfate (PMS). It was found that ACs were effective in heterogeneous activation of PMS to produce sulfate radicals for degradation of phenol, much better than H2O2 and PS. Particle size of AC significantly influenced AC activity, and powder AC was much more effective than granular AC. The complete phenol removal could be achieved in 15 min on powder activated carbon (PAC) under the conditions of [phenol] = 25 mg L−1, [PAC] = 0.2 g L−1, [PMS] = 6.5 mmol L−1, and T = 25 °C. It was also found that phenol degradation was significantly influenced by PMS loading, catalyst loading, phenol concentration and temperature. Surface activation of PMS and phenol adsorption played important roles in phenol degradation. Surface coverage by intermediate adsorption and structural change induced deactivation of AC and catalytic activity could be partially recovered by regeneration using calcination.

Heterogeneous activation of peroxymonosulphate by supported ruthenium catalysts for phenol degradation in water

Activated carbon (AC) and Zeolite Socony Mobil-5 (ZSM5) supported ruthenium oxide catalysts were prepared and tested to degrade aqueous phenol in the presence of peroxymonosulphate. The physicochemical properties of ruthenium oxide based catalysts were characterised by several techniques such as XRD (X-ray diffraction), SEM-EDS (scanning electron microscopy-energy dispersive X-ray spectroscopy), and N(2) adsorption. It was found that RuO(2)/AC was highly effective in heterogeneous activation of peroxymonosulphate to produce sulphate radicals, presenting higher reaction rate in phenol degradation compared with RuO(2)/ZSM-5. Degradation efficiency of phenol could be achieved at 100% of phenol decomposition and 60% of total organic carbon (TOC) removal in 1h at the conditions of 50ppm phenol, 0.2g catalyst, 1g Oxone(®) in 500mL solution at 25°C using the two catalysts. It was also found that phenol degradation was strongly influenced by catalyst loading, phenol concentration, Oxone(®) concentration and temperature. Kinetic studies proved that a pseudo first order kinetics would fit to phenol decomposition and the activation energies for RuO(2)/AC and RuO(2)/ZSM5 were obtained to be 61.4 and 42.2kJ/mol, respectively.