Aluminum is a kind of metal that we often encounter. It can also be absorbed by the human body invisibly and will affect our bodies to a certain extent, e.g., by causing symptoms associated with Alzheimer’s disease. Therefore, the detection of aluminum is particularly important. The methods to detect metal ions include precipitation methods and electrochemical methods, which are cumbersome and costly. Fluorescence detection is a fast and sensitive method with a low cost and non-toxicity. Traditional fluorescent nanomaterials have a high cost, high toxicity, and cause harm to the human body. Graphene quantum dots are a new type of fluorescent nanomaterials with a low cost and non-toxicity that can compensate for the defects of traditional fluorescent nanomaterials. In this paper, c-GQDs and o-GQDs with good performance were prepared by a bottom-up hydrothermal method using o-phenylenediamine as a precursor and citric acid or boric acid as modulators. They have very good optical properties: o-GQDs exhibit orange fluorescence under UV irradiation, while c-GQDs exhibits cyan fluorescence. Then, different metal ions were used for ion detection, and it was found that Al³⁺ had a good quenching effect on the fluorescence of the o-GQDs. The reason for this phenomenon may be related to the strong binding of Al³⁺ ions to the N and O functional groups of the o-GQDs and the rapid chelation kinetics. During the chelation process, the separation of o-GQDs’ photoexcited electron hole pairs leads to their rapid electron transfer to Al³⁺, in turn leading to the occurrence of a fluorescence-quenching phenomenon. In addition, there was a good linear relationship between the concentration of the Al³⁺ ions and the fluorescence intensity, and the correlation coefficient of the linear regression equation was 0.9937. This illustrates the potential for the wide application of GQDs in sensing systems, while also demonstrating that Al³⁺ sensors can be used to detect Al³⁺ ions.

Biological imaging is an essential means of disease diagnosis. However, semiconductor quantum dots that are used in bioimaging applications comprise toxic metal elements that are nonbiodegradable, causing serious environmental problems. Herein, we developed a novel ecofriendly solvothermal method that uses ethanol as a solvent and doping with chlorine atoms to prepare highly fluorescent graphene quantum dots (GQDs) from seaweed. The GQDs doped with chlorine atoms exhibit high-intensity white fluorescence. Thus, their preliminary application in bioimaging has been confirmed. In addition, clear cell imaging could be performed at an excitation wavelength of 633 nm.

Due to the rapid development of industrialization, various environmental problems such as water resource pollution are gradually emerging, among which heavy metal pollution is harmful to both human beings and the environment. As a result, there are many metal ion detection methods, among which fluorescence detection stands out because of its rapid, sensitive, low cost and non-toxic characteristics. In recent years, graphene quantum dots have been widely used and studied due to their excellent properties such as high stability, low toxicity and water solubility, and have a broad prospect in the field of metal ion detection. A novel high fluorescence Cu²⁺, Co²⁺ sensing probe produced by graphene quantum hydrothermal treatment is reported. After heat treatment with hydrazine hydrate, the small-molecule precursor nitronaphthalene synthesized by self-nitrification was transformed from blue fluorescent GQDs to green fluorescent amino-functionalized N–GQDs. Compared with other metal ions, N–GQDs are more sensitive to Cu²⁺ and Co²⁺ on the surface, and N–GQDs have much higher selectivity to Cu²⁺ and Co²⁺ than GQDs. The strategy proposed here is simple and economical in design.

Industrial dye wastewater poses serious environmental and health risks, demanding sustainable remediation strategies. Here, hierarchically porous hollow TiO₂ nanofibers (HNFTis) were fabricated and combined with blue, green, and orange graphene quantum dots (b-GQDs, g-GQDs, o-GQDs) to form heterojunction photocatalysts. Progressive fluorescence redshift of GQDs, induced by surface functionalization and S/B doping, narrows the bandgap and enhances visible-light absorption. Among the composites, 0.5 wt% o-GQDs/HNFTi exhibited the highest photocurrent and lowest charge-transfer resistance and degraded 99.5% of Methylene blue under visible light within 2 h, outperforming pristine HNFTi (77.7%). The synergistic effect of TiO₂ structural engineering and GQD fluorescence tuning demonstrates an effective strategy for designing high-performance photocatalysts for sustainable wastewater treatment.

Industrial dye wastewater poses severe environmental and health risks, creating an urgent demand for efficient and sustainable remediation technologies. Herein, hierarchically porous hollow TiO2 nanofibers (HNFTi) were constructed through electrospinning and coupled with blue-, green-, and orange-emissive graphene quantum dots (b-, g-, and o-GQDs) to fabricate visible-light-responsive heterojunction photocatalysts. By tailoring the surface functional groups and heteroatom doping of GQDs, a progressive fluorescence redshift was achieved, which effectively narrowed the bandgap and extended visible-light absorption. Benefiting from the synergistic effects of the hierarchically porous hollow TiO2 architecture and the fluorescence-tuned GQDs, the resulting composites exhibited enhanced light harvesting, accelerated charge separation, and improved interfacial charge transfer. Among them, the 0.5 wt% o-GQDs/HNFTi composite showed the best photocatalytic performance, delivering a methylene blue degradation efficiency of 99.5% within 2 h under visible-light irradiation, markedly higher than that of pristine HNFTi (77.7%). Photoelectrochemical and Kelvin probe force microscopy analyses further confirmed the promoted carrier dynamics and effective interfacial separation of photogenerated electron-hole pairs. This work provides a feasible strategy for integrating structural engineering and fluorescence modulation to develop high-performance TiO2-based photocatalysts for wastewater treatment.