Composites of synthesized reduced graphene oxide (rGO) and titanium dioxide nanotubes (TNTs) were examined and combined at different mass proportions (3:1, 1:1, and 1:3) to develop an electrochemical double layer capacitor (EDLC) nanocomposite. Three different combination methods of synthesis—(1) TNT introduction during GO reduction, (2) rGO introduction during TNT formation, and (3) TNT introduction in rGO sheets using a microwave reactor—were used to produce nanocomposites. Among the three methods, method 3 yielded an EDLC nanomaterial with a highly rectangular cyclic voltammogram and steep electrochemical impedance spectroscopy plot. The specific capacitance for method 3 nanocomposites ranged from 47.26–165.22 F/g while that for methods 1 and 2 nanocomposites only ranged from 14.03–73.62 F/g and 41.93–84.36 F/g, respectively. Furthermore, in all combinations used, the 3:1 graphene/titanium dioxide-based samples consistently yielded the highest specific capacitance. The highest among these nanocomposites is 3:1 rGO/TNT. Characterization of this highly capacitive 3:1 rGO/TNT EDLC composite revealed the dominant presence of partially amorphous rGO as seen in its XRD and SEM with branching crystalline anatase TNTs as seen in its XRD and TEM. Such property showed great potential that is desirable for applications to capacitive deionization and energy storage.

Death due to diseases from poor sanitation is a serious global issue and it has become one of the priorities of the United Nations’ Sustainable Development Goals (i.e., SDG6). This SDG6 aims to provide adequate improved sanitation facilities to over 2.3 billion people around the world who have no or limited access to sanitation, wherein more than two-thirds of these un-served people live in rural areas. One of the strategies for addressing this global issue is through emerging sustainable sanitation technologies such as the Eco-Toilet System (ETS), which uses small amounts of water or is even waterless and recovers nutrients from human waste thereby promoting water-energy conservation, improved sanitation and supplement nutrients essential to plant growth. Social acceptance, however, remains a key barrier in deploying the ETS. A social perception study on the use of the ETS was conducted in a rural community in Mulanay, Philippines. The researchers analyzed the proposed combined technology acceptance model and theory of planned behavior (C-TAM-TPB) using multiple linear regression and the Mann-Whitney U-test to evaluate the perceptions and attitudes of a rural community towards the use of the ETS. The results showed that more than 50% of the respondents are aware of the nutrient value of human excreta and believe that it is usable as fertilizer; however, less than 25% prefer to utilize it for food production. Results also indicate that the behavior of the users is driven by their attitude (β = 0.420, p-value < 0.010). Moreover, the Mann-Whitney U-test results revealed that people who are knowledgeable of the nutrient value of human excreta and are willing to collect them have more positive attitude towards the ETS.

Carbon dioxide sequestration via mineralization is one of the methods that has the capability to efficiently store carbon dioxide in a stable form. A mixed dump sample collected from a nickel laterite mine in Southern Philippines was tested for its carbon dioxide sequestration potential through HCl leaching tests, employing the Face-Centered Cube (FCC) experimental design for Response Surface Methodology (RSM). Mineralogical analysis performed through X-ray diffraction (XRD) analysis suggests the presence of three minerals, namely goethite, khademite and lizardite; additional X-ray fluorescence (XRF) and inductively-coupled plasma optical emission spectroscopy (ICP-OES) results, however, established goethite as the main component due to the dominance of iron in the sample. Morphological analyses performed through a scanning electron microscope (SEM) and the Brunauer–Emmett–Teller (BET) method suggest high accessible surface area despite considerable variability in sample composition. Leaching tests further confirmed the high reactivity of the mixed dump as high extraction rates were obtained for iron, with the maximum iron extraction efficiency of 95.37% reported at 100 °C, 2.5 M, and 2.5 h. The carbon dioxide sequestration potential of the mixed dump was reported as the amount of CO₂ that can be sequestered per amount of sample, which was calculated to be 327.2 mg CO_2/g sample using the maximum iron extraction obtained experimentally.

This research aimed to utilize the concentrated brine by incorporating a forward osmosis (FO) system as a post-treatment in a reverse osmosis (RO) plant. The objective of this study was to optimize the operating condition of an FO system utilizing RO brine. Water flux and reverse solute flux were measured at different draw solution (DS) concentrations. Change in the salinity of the feed and permeate flux are the two parameters that were monitored and evaluated. To further optimize the process, membrane fouling was also investigated. Fouled membrane was subjected to scanning electron microscopy and energy dispersive X-ray analyses. Seawater was used as the feed while sodium chloride was used to simulate different brine concentrations. It was observed that increasing the concentration of brine enhances permeate flux. However, increase in reverse solute flux was also observed compensating the high water flux. Fouling in the support layer of FO membrane was evident at 200 g/L DS concentration. While 100 g/L was found to be the most suitable for FO system with almost similar fouling propensity as compared to 50 and 75 g/L. With lower internal concentration polarization and optimized operating condition, FO system could be efficiently used in utilizing RO brine.

The capability of novel 3:1 reduced graphene oxide/titanium dioxide nanotubes (rGO/TiONTs) composite to desalinate using capacitive deionization (CDI) employing highly concentrated NaCl solutions was tested in this study. Parameters such as material wettability, electrosorption capacity, charge efficiency, energy consumption, and charge-discharge retention were tested at different NaCl initial concentrations—100 ppm, 2000 ppm, 15,000 ppm, and 30,000 ppm. The rGO/TiONTs composite showed good material wettability before and after CDI runs with its contact angles equal to 52.11° and 56.07°, respectively. Its two-hour electrosorption capacity during CDI at 30,000 ppm NaCl influent increased 1.34-fold compared to 100 ppm initial NaCl influent with energy consumption constant at 1.11 kWh per kg with NaCl removed. However, the percentage discharge (concentration-independent) at zero-voltage ranged from 4.9–7.27% only after 30 min of desorption. Repeated charge/discharge at different amperes showed that the slowest charging rate of 0.1 A·g⁻¹ had the highest charging time retention at 60% after 100 cycles. Increased concentration likewise increases charging time retention. With this consistent performance of a CDI system utilizing rGO/TiONTs composite, even at 30,000 ppm and 100 cycles, it can be a sustainable alternative desalination technology, especially if a low charging current with reverse voltage discharge is set for a longer operation.

The potential utilization of waste rock obtained from an active nickel mine site in Mindanao, the Philippines for indirect carbon sequestration is explored in this study. X-ray diffraction (XRD), X-ray fluorescence (XRF), and inductively coupled plasma optical emission spectroscopy (ICP-OES) results showed that the sample is rich in iron, existing in three different forms: goethite (α-FeOOH), chromite (FeCr₂O₄), and magnetite (Fe₃O₄). Leaching tests performed using hydrochloric acid (HCl) showed high iron extraction rates, with a maximum average extraction efficiency of 95.35% obtained at 100°C, 4 M HCl, and 1.0 h. Morphological and physicochemical analyses conducted through scanning electron microscopy and Brunauer–Emmett–Teller (BET) method supported the high extraction rates obtained for Fe, which is due to the higher reactivity of the sample to the leaching agent as well as the higher availability of accessible sites for reaction on the sample surface as compared to other mine wastes that are previously utilized. The nickel laterite waste rock sample has the potential to be used as a feedstock for iron carbonation in indirect carbon sequestration; however, challenges such as the use of sulfide source and cost requirements must be addressed in order to fully determine its viability for industrial scale application.