A Laser-Induced Graphene-Titanium(IV) Oxide Composite for Adsorption Enhanced Photodegradation of Methyl Orange.

Numerous treatment methods such as biological digestion, chemical oxidation, and coagulation have been used to treat organic micropollutants. However, such wastewater treatment methods can be either inefficient, expensive, or environmentally unsound. Here, we embedded TiO2 nanoparticles in laser-induced graphene (LIG) and obtained a highly efficient photocatalyst composite with pollutant adsorption properties. TiO2 was added to LIG and lased to form a mixture of rutile and anatase TiO2 with a decreased band gap (2.90 ± 0.06 eV). The LIG/TiO2 composite adsorption and photodegradation properties were tested in solutions of a model pollutant, methyl orange (MO), and compared to the individual and mixed components. The adsorption capacity of the LIG/TiO2 composite was 92 mg/g using 80 mg/L MO, and together the adsorption and photocatalytic degradation resulted in 92.8% MO removal in 10 min. Adsorption enhanced photodegradation, and a synergy factor of 2.57 was seen. Understanding how LIG can modify metal oxide catalysts and how adsorption can enhance photocatalysis might lead to more effective pollutant removal and offer alternative treatment methods for polluted water.

Laser-Induced Graphene Capacitive Killing of Bacteria.

Laser-induced graphene (LIG) is a method of generating a foam-like conformal carbon layer of porous graphene on many types of carbon-based surfaces. This electrically conductive material has been shown to be useful in many applications including environmental technology and includes low fouling and antimicrobial surfaces and can address persistent environmental challenges spawned by bacterial and viral contaminates. Here, we show that a single film of LIG stores charge when an electrical current is applied and dissipates charge when the current is stopped, which results in electricidal surface antibacterial potency. The amount of accumulated and dissipated charge on a single strip of LIG was quantified with an electrometer by generating LIG on both sides of a nonconducting polyimide film, which showed up to 65 pC of charge when the distance between the surfaces was 94 µm corresponding to an areal capacitance of 1.63 pF/cm2. We further corroborate the stored charge decay of a single LIG strip with bacteria death via direct electrical contact. Antimicrobial rates decreased with the same monotonic pattern as the loss of charge from the LIG film (i.e., AR ∼ 97% 0 s after voltage source disconnection vs AR ∼ 21% 90 s after disconnection) showing bacterial death as a function of delayed LIG exposure time after applied voltage disconnection. In terms of energy efficiency, this translates to an increased bacteria potency of ∼170% for the equivalent energy costs as that previously estimated. Finally, we present a mechanistic explanation for the capacitive behavior and the electricidal effects for a single plate of LIG.