Without pure water, it is impossible to survive for any living beings. The ratio of freshwater on our planet is very poor and the demand is increasing with time for the growing population. Furthermore, water is being contaminated by industrial and agricultural activities, pharmaceuticals, technocratic civilization, pesticides, garments, global changes etc. In addition to this, environmental pollution and global warming are swelling due to the greenhouse and harmful gases generated from the dumping and burning of fossil fuel. Addressing these problems, it is necessary to find out the cost-effective and environmental friendly processes to purify the contaminated water and air. Activated carbons (ACs) are one of the best solutions for removing the pollutants from aqueous and atmosphere as it is the carbonaceous materials with a high degree of porosity, well-developed surface area, and distinguished functional groups which are required for elimination of contaminants. The preparations of activated carbon are easy and safe processes, mainly from the pyrolysis or gasification of biomass with heat and/or chemicals. The recycling and regeneration of activated carbon after use are also essential for resource maintenance and environmental safety. Thus, AC can protect the ecosystem in a double direction by purifying the water and air from the pollutants.

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Pennisetum purpureum is one of the most invasive perennial grasses of the Poaceae family, which are abundant in southeast Asia including Brunei Darussalam. The pyrolysis process at a slow heating rate proved to be highly promising for biochar production. The production and characterization of different Pennisetum purpureum biochars have been investigated at the pyrolysis temperatures of 400 °C, 500 °C and 600 °C with a heating and nitrogen flow rate of 5 °C/min and 0.5 L/min, respectively. The observed higher heating values were 22.18 MJ/kg, 23.02 MJ/kg, 23.75 MJ/kg, and the alkaline pH were 9.10, 9.86, 10.17 for the biochar at 400 °C, 500 °C, 600 °C temperatures, respectively. The water holding capacity was one hundred percent for all biochars and continued to increase for higher pyrolysis temperature. SEM images show that the porosity of the biochars has been enhanced with increased temperatures due to the rearrangement of crystallinity and aromaticity. On the other hand, the yields of biochar have been decreased from 35.13% to 23.02% for the increase of pyrolysis temperature from 400 °C to 600 °C. Energy dispersive X-ray analysis shows that the O/C atomic ratios were 0.15, 0.08 and 0.06 for the biochar of 400, 500 and 600 °C which validates the improvement in heating values. FT-IR analysis revealed that the available functional groups in the biochars were CO , C=C, and C-H. Thermogravimetric analysis (TGA) under pyrolysis condition showed residue of 46.56%, 51.13% and 55.67% from the biochar at 400, 500, and 600 °C, respectively. The derivative thermogravimetry (DTG) graph indicates that the degradation rate is higher for 400 °C biochar than the 600 °C biochar.

To evaluate the possibilities for biofuel and bioenergy production Acacia Holosericea, which is an invasive plant available in Brunei Darussalam, was investigated. Proximate analysis of Acacia Holosericea shows that the moisture content, volatile matters, fixed carbon, and ash contents were 9.56%, 65.12%, 21.21%, and 3.91%, respectively. Ultimate analysis shows carbon, hydrogen, and nitrogen as 44.03%, 5.67%, and 0.25%, respectively. The thermogravimetric analysis (TGA) results have shown that maximum weight loss occurred for this biomass at 357 °C for pyrolysis and 287 °C for combustion conditions. Low moisture content (<10%), high hydrogen content, and higher heating value (about 18.13 MJ/kg) makes this species a potential biomass. The production of bio-char, bio-oil, and biogas from Acacia Holosericea was found 34.45%, 32.56%, 33.09% for 500 °C with a heating rate 5 °C/min and 25.81%, 37.61%, 36.58% with a heating rate 10 °C/min, respectively, in this research. From Fourier transform infrared (FTIR) spectroscopy it was shown that a strong C–H, C–O, and C=C bond exists in the bio-char of the sample.

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