Amorphous Ni(OH)2 nanocages as efficient SERS substrates for selective recognition in mixtures

Surface-enhanced Raman scattering (SERS) technology has become one of the most powerful tools for identifying trace analytes due to its outstanding merit of fingerprint spectrum. It has been found that noble metal (Ag, Au) materials can produce obvious surface plasmon resonance under visible light illumination, which can bring out a strong SERS effect. However, due to poor stability and non-selectivity, its practical applications are seriously hindered, especially for the detection of polluted water contaminating mixture organic pollutants. Herein, we designed an amorphous Ni(OH) 2 nanocages (a-Ni(OH) 2 NCs) substrate that exhibits an excellent SERS performance with good spectral stability and selectivity, which is attributed to the strong interfacial photo-induced charge transfer (PICT) mechanism between a-Ni(OH) 2 NCs and molecules. Due to the effective vibrational coupling of a-Ni(OH) 2 NCs and molecule under laser irradiation, the PICT transitions between a-Ni(OH) 2 NCs and molecules evidently increase the molecular polarizability tensor and magnify molecular Raman scattering cross-section, resulting in a remarkable SERS activity. Besides, in wastewater containing several nitrogen and phosphorus pollutants, we successfully identified methylene blue and crystal violet molecules by using a-Ni(OH) 2 NCs due to their selective recognition function. This research points out a new application direction for SERS technology in water pollution detection based on non-metal substrates, which widely broadens application prospects of SERS spectroscopy. • High-SERS-performance amorphous Ni(OH) 2 nanocages were successfully synthesized. • a-Ni(OH) 2 NCs possess large specific surface area and optical resonance cavities. • Amorphous nanomaterials favor photo-induced charge transfer (PICT) mechanism. • a-Ni(OH) 2 SERS substrates possess selective recognition function in mixed wastewater.