# Arginine-Mediated Self-Assembly of Porphyrin on Graphene: A Photocatalyst for Degradation of Dyes
## 3 Results  
Figure 2A shows the SEM image of GNPs obtained from VNsgraphene. It is clear that the GNPs have a wrinkled, crumpled structure with a lateral diameter of tens of microns. The semitransparency of GNPs to the electron beam also suggests that the thickness of GNPs is approximately 5-15 nm [40]. Figure 2B is the SEM image of free-standing arginine-mediated self-assembly of porphyrins dropped onto a silicon wafer. The assembled porphyrins have similar morphology to our previous work [27], which is best described as a belt-like morphology several microns in length, with diameters of about 20-30 nm. Figure 1: Schematic diagram of arginine-mediated self-assembly of porphyrin nanofibers on graphene surface. The morphology and distribution of the arginine-mediated self-assembly porphyrin TCPP on the graphene are observed by SEM and TEM images in Figure 3, Figures S1 and S2. It is seen that the porphyrins nanofibers were densely and uniformly distributed on the surface of the GNPs with a diameter ranging from 50 to 200 nm and several micrometers in length. In contrast to Arginine-assisted self-assembly of TCPP with GNPs, which demonstrated the formation of well-dispersed porphyrin nanorods with 50-100 nm in diameter and about 200 nm in length on the GNPs surface [38], in this case the diameter of the TCPP aggregates are almost unchanged. This suggests that the presence of arginine helps to elongate the aggregation of TCPP to form nanofibers with length on the micron scale. Figure 4A shows the UV-vis spectra of monomeric TCPP molecules, free-standing TCPP aggregates and GNPs@TCPP nanofibers. The absorption spectrum of the TCPP monomer shows a strong peak at 414 nm, namely a Soret absorption, as a result of a transition from a1u (\(\pi\)) to e\({}^{*}_{g}\) (\(\pi\)), and four weak peaks ranging from 500 to 700 nm, which are ascribed to Q bands of the a2u (\(\pi\)) to e\({}^{*}_{g}\) (\(\pi\)) transition [24, 41]. Free-standing TCPP aggregates in the presence of arginine reveal a Soret absorption peak at 417 nm and the four weak absorption peaks of Q bands in the TCPP monomer are replaced by a strong peak at 666 nm also with three weak Q-bands in its original TCPP. The distinct bathochromic and hypsochromic shifts by 3 nm in Soret band of the TCPP confirm aggregation formation in comparison with monomeric TCPP, which indicates that most of the TCPP building blocks form \(J\)-type supramolecular assemblies with induction of arginine [15, 37, 42]. Similarly, the UV-vis spectrum of GNPs@TCPP nanofibers also show a Soret peak at approximately 420 nm and one strong peak at 666 nm along with three relatively weak peaks in Q-band region. The presence of graphene in this case is responsible for larger bathochromic and hypsochromic shifts, which is  
Figure 3: (**A**) Low and (**B**) high-resolution SEM images of arginine-induced self-assembly of TCPP on the graphene surface, respectively. Figure 2: Scanning electron microscopy (SEM) images of (**A**) graphene nanoplates, (**B**) free-standing arginine-induced tetrakis (4-carboxyphenyl) porphyrin (TCPP) aggregates. about 6 nm. A broad peak at around 350 nm, which is attributed to the characteristic absorbance of grapheme [43]. The change in the Q-band region is evident in four weak peaks in the absorbance of monomeric TCPP changing to one strong peak along with three relatively weak peaks (inset in Figure 4A) GNPs@TCPP nanofibers. This also support our hypothesis of \(J\)-type assemblies of TCPP monomers on the GNPs surface. The optical properties of TCPP nanofibers on GNPs were further investigated by photoluminescence (Figure 4B). The fluorescence spectrum of TCPP in aqueous solution shows one characteristic emission peak at 669 nm. Interestingly, the photoluminescence spectrum of free-standing TCPP nanobelts and GNPs@TCPP nanofibers show relatively weak and broad emission peaks at approximately 730 and 686 nm, respectively.