A state-of-the-art review of metal oxide nanoflowers for wastewater treatment: Dye removal.

Dye wastewater consists of high solids concentrations, heavy metals, minor contaminants, dissolved chemical oxygen demand, and microorganisms. Nanoflowers are nanoparticles that resemble flowers when viewed at a microscopic level. Inorganic metal oxide nanoflowers have been discovered to be a potential source for overcoming this situation. Their flower-like features give them a higher surface area to volume ratio and porosity structure, which can absorb a significant amount of dye. The metal oxide nanoflower synthesized from different synthesis methods is used to compare which one is cost-effective and capable of generating a large scale of nanoflower. This review has demonstrated outstanding dye removal efficiency by applying inorganic nanoflowers to dye removal. Since both adsorption and photocatalytic reactions enhance the dye degradation process, complete dye degradation could be achieved. Meanwhile, the inorganic metal oxide nanoflowers' exemplary reusability characteristics with negligible performance drop further prove that this approach is highly sustainable and may help to save costs. This review has proven the momentum of obtaining high dye removal efficiency in wastewater treatment to conclude that the metal oxide nanoflower study is worth researching.

Techno-economic assessment of hydrotreated vegetable oil as a renewable fuel from waste sludge palm oil.

To date, the development of renewable fuels has become a normal phenomenon to solve the problem of diesel fuel emissions and the scarcity of fossil fuels. Biodiesel production has some limitations, such as two-step processes requiring high free fatty acids (FFAs), oil feedstocks and gum formation. Hydrotreated vegetable oil (HVO) is a newly developed international renewable diesel that uses renewable feedstocks via the hydrotreatment process. Unlike FAME, FFAs percentage doesn't affect the HVO production and sustains a higher yield. The improved characteristics of HVO, such as a higher cetane value, better cold flow properties, lower emissions and excellent oxidation stability for storage, stand out from FAME biodiesel. Moreover, HVO is a hydrocarbon without oxygen content, but FAME is an ester with 11% oxygen content which makes it differ in oxidation stability. Waste sludge palm oil (SPO), an abundant non-edible industrial waste, was reused and selected as the feedstock for HVO production. Techno-economical and energy analyses were conducted for HVO production using Aspen HYSYS with a plant capacity of 25,000 kg/h. Alternatively, hydrogen has been recycled to reduce the hydrogen feed. With a capital investment of RM 65.86 million and an annual production cost of RM 332.56 million, the base case of the SPO-HVO production process was more desirable after consideration of all economic indicators and HVO purity. The base case of SPO-HVO production could achieve a return on investment (ROI) of 89.03% with a payback period (PBP) of 1.68 years. The SPO-HVO production in this study has observed a reduction in the primary greenhouse gas, carbon dioxide (CO2) emission by up to 90% and the total annual production cost by nearly RM 450 million. Therefore, SPO-HVO production is a potential and alternative process to produce biobased diesel fuels with waste oil.

Potential heterogeneous nano-catalyst via integrating hydrothermal carbonization for biodiesel production using waste cooking oil.

Hydrothermal carbonization (HTC) provides alternatives technique to produce a nanosize activated carbon from biomass with a high surface area. Herein, this study we prepared empty fruit bunch-based activated carbon (EFBHAC) using HTC technique. The activated carbon was then functionalized with K2CO3 and Cu(NO3)2 to produce bifunctional nano-catalyst for simultaneous esterification-transesterification of waste cooking oil (WCO). The physicochemical properties were performed i.e. N2 sorptions analysis, TPD-CO2/NH3, FESEM, EDX, FTIR and XRD analysis. The results revealed that produced EFBHAC possessed a BET surface area of 4056.17 m2 g-1, with pore volume of 0.827 cm3 g-1 and 5.42 nm of pore diameter resulting from hydrolysis, dehydration decarboxylation, aromatization and re-condensation during HTC process. Impregnation of EFBHAC with K2CO3 and Cu(NO3)2 granted a high amount of basicity and acidity of 9.21 mmol g-1 and 31.41 mmol g-1, respectively, accountable to high biodiesel yield of 97.1%, produced at the optimum condition of 5 wt% of catalyst loading, 12:1 of methanol to oil molar ratio at 70 °C for 2 h. More than 80% of biodiesel was produced after the 5th cycle depicted the good reusability. The transformations from WCO to biodiesel was confirmed via 1H NMR, FTIR and TGA analysis. Fuel properties revealed kinematic viscosity of 3.3 mm2 s-1, cetane number of 51, flash point of 160.5 °C, cloud and pour point of 11 °C and -3 °C, respectively. These results show the excellent potential of waste materials to prepare bifunctional nano-catalysts to produce higher biodiesel yield which has potential to be commercialized.

Novel micro-structured carbon-based adsorbents for notorious arsenic removal from wastewater.

The contamination of groundwater by arsenic (As) in Bangladesh is the biggest impairing of a population, with a large number of peoples affected. Specifically, groundwater of Gangetic Delta is alarmingly contaminated with arsenic. Similar, perilous circumstances exist in many other countries and consequently, there is a dire need to develop cost-effective decentralized filtration unit utilizing low-cost adsorbents for eliminating arsenic from water. Morphological synthesis of carbon with unique spherical, nanorod, and massive nanostructures were achieved by solvothermal method. Owing to their intrinsic adsorption properties and different nanostructures, these nanostructures were employed as adsorption of arsenic in aqueous solution, with the purpose to better understanding the morphological effect in adsorption. It clearly demonstrated that carbon with nanorods morphology exhibited an excellent adsorption activity of arsenite (about 82%) at pH 3, remarkably superior to the two with solid sphere and massive microstructures, because of its larger specific surface area, enhanced acid strength and improved adsorption capacity. Furthermore, we discovered that iron hydroxide radicals and energy-induced contact point formation in nanorods are the responsible for the high adsorption of As in aqueous solution. Thus, our work provides insides into the microstructure-dependent capability of different carbon for As adsorption applications.

Synthesis of bifunctional nanocatalyst from waste palm kernel shell and its application for biodiesel production.

The potential of bifunctional nanocatalysts obtained from waste palm kernel shell (PKS) was investigated for one-step transesterification-esterification under mild conditions. State-of-the-art characterization illustrated that the synthesized catalyst has high stability through the thermal test, high BET surface area of 438.08 m2 g-1, pore volume of 0.367 cm3 g-1 and pore width of 3.8 nm. The high amount of basicity (8.866 mmol g-1) and acidity (27.016 mmol g-1) promoted the successfulness of simultaneous transesterification-esterification. The investigation revealed that the combination of potassium and copper on activated carbon surface showed good catalytic activity by giving 95.0% FAME yield and 97.3% FFA conversion at a relatively mild condition of 5 wt% catalyst loading, 12 : 1 methanol to oil molar ratio at 80 °C for 4 hours with FAME yield > 80% after 5 reaction cycles. Characterization of the spent catalyst showed that the amount of basicity was reduced to 3.106 mmol g-1, which validated the reduction of the catalytic performance. The usage of waste material was successfully discovered in producing an effective bifunctional catalyst for biodiesel production from waste cooking oil (WCO) and has high potential for commercialization in the future.

Sulfonated SnO2 nanocatalysts via a self-propagating combustion method for esterification of palm fatty acid distillate.

Biodiesel derived from palm fatty acid distillate (PFAD) was produced via catalytic esterification using sulfonated tin oxide (HSO3 -/SnO2) as the superacid solid catalyst. In this work, the SnO2 catalyst was synthesised by the self-propagating combustion (SPC) method, and activated using chlorosulfonic acid. The SPC method was able to produce nano-sized particles with homogenous size and shape that were anchored with many HSO3 - ions, resulting in more exceptional acid properties that effectively esterified the PFAD feedstock into FAMEs (fatty acid methyl esters). Several studies based on metal oxide-based catalysts were also included for comparison. Under the optimised conditions of 9 : 1 (methanol-to-PFAD molar ratio), 4 wt% (catalyst loading), 100 °C (reaction temperature) and 3 h (reaction time), the FFA conversion and FAME yield were 98.9% and 93.8%, respectively. Besides, the sulfonated SnO2-spc catalyst can be reused in up to five consecutive cycles with an acceptable esterification performance and minimal sulfur leaching. It is worth mentioning that the SPC method is a greener and simpler technique to obtain the nanocatalysts. Overall, the production of FAME from low value, cheaper, abundant, and non-edible PFAD feedstock, assisted by a non-transition metal oxide of sulfonated SnO2 catalyst, could reduce the cost of biodiesel production.

Development of bimetallic nickel-based catalysts supported on activated carbon for green fuel production.

In this work, the catalytic deoxygenation of waste cooking oil (WCO) over acid-base bifunctional catalysts (NiLa, NiCe, NiFe, NiMn, NiZn, and NiW) supported on activated carbon (AC) was investigated. A high hydrocarbon yield above 60% with lower oxygenated species was found in the liquid product, with the product being selective toward n-(C15 + C17)-diesel fractions. The predominance of n-(C15 + C17) hydrocarbons with the concurrent production of CO and CO2, indicated that the deoxygenation pathway proceeded via decarbonylation and decarboxylation mechanisms. High deoxygenation activity with better n-(C15 + C17) selectivity over NiLa/AC exposed the great synergistic interaction between La and Ni, and the compatibility of the acid-base sites increased the removal of oxygenated species. The effect of La on the deoxygenation reaction performance was investigated and it was found that a high percentage of La species would be beneficial for the removal of C-O bonded species. The optimum deoxygenation activity of 88% hydrocarbon yield with 75% n-(C15 + C17) selectivity was obtained over 20% of La, which strongly evinced that La leads to a greater enhancement of the deoxygenation activity. The NiLa/AC reusability study showed consistent deoxygenation reactions with 80% hydrocarbon yield and 60% n-(C15 + C17) hydrocarbon selectivity within 6 runs.

Single-Pot Synthesis of Biodiesel using Efficient Sulfonated-Derived Tea Waste-Heterogeneous Catalyst.

The main purpose of this manuscript is to report the new usage of tea waste (TW) as a catalyst for efficient conversion of palm fatty acid distillate (PFAD) to biodiesel. In this work, we investigate the potential of tea waste char as a catalyst for biodiesel production before and after sulfonation. The activated sulfonated tea waste char catalyst was characterized using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffractometry (XRD), elemental composition (CHNS), nitrogen adsorption-desorption using Brunauer-Emmett-Teller (BET) and ammonia-temperature-programmed desorption (NH3-TPD). The activated tea waste char catalyst shows higher acid density of 31 µmol g-1 as compared to tea waste char of 16 µmol g-1 and higher surface area of 122 m2/g. The optimum fatty acid conversion conditions were found that 4 wt % of catalyst loading with 9:1 of methanol:PFAD for 90 min of reaction time at 65 °C gives 97% free fatty acid (FFA) conversion. In conclusion, the sulfonated tea waste (STW) catalyst showed an impressive catalytic activity towards the esterification of PFAD at optimum reaction conditions with significant recyclability in five successive cycles without any reactivation step.